UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

FORM 6-K

REPORT OF FOREIGN PRIVATE ISSUER

PURSUANT TO RULE 13a-16 OR 15d-16 UNDER

THE SECURITIES EXCHANGE ACT OF 1934

For the month of March 2020

Commission File Number: 001-35126

21Vianet Group, Inc.

Guanjie Building, Southeast 1st Floor

10# Jiuxianqiao East Road

Chaoyang District

Beijing 100016

The People’s Republic of China

(86 10) 8456 2121

(Address, including zip code, and telephone number, including area code, of Registrant’s principal executive offices)

Indicate by check mark whether the registrant files or will file annual reports under cover of Form 20-F or Form 40-F.

Form 20-F  ☒             Form 40-F  ☐

Indicate by check mark if the registrant is submitting the Form 6-K in paper as permitted by Regulation S-T Rule 101(b)(1):  ☐

Indicate by check mark if the registrant is submitting the Form 6-K in paper as permitted by Regulation S-T Rule 101(b)(7):  ☐

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized.

Date: March 6, 2020

Exhibit Index

Exhibit 99.1 — Press Release

Exhibit 99.1

21Vianet Group, Inc. Reports Unaudited Fourth Quarter and Full Year 2019 Financial Results

BEIJING, March 4, 2020 (GLOBE NEWSWIRE) - 21Vianet Group, Inc. (Nasdaq: VNET) (“21Vianet” or the “Company”), a leading carrier- and cloud-neutral Internet data center services provider in China, today announced its unaudited financial results for the fourth quarter ended December 31, 2019. The Company will hold a conference call at 8:00 P.M. on Wednesday, March 4, 2020, U.S. Eastern Time to discuss the financial results. Dial-in details are provided at the end of this release.

Fourth Quarter 2019 Financial Highlights

Full Year 2019 Financial Highlights

Fourth Quarter 2019 Operational Highlights

Mr. Alvin Wang, Chief Executive Officer and President of the Company, stated, “2019 was a productive year for 21Vianet as we met both our capacity expansion and financial targets. Notably, during the quarter, we signed a memorandum of understanding with an industry-leading wholesale customer, marking a significant milestone for the company and illustrating the attractiveness of our IDC services for large-scale clients. Moreover, during the quarter, we continued to see strong demand from our retail customers for both scalable space and turn-key hybrid IT solutions. As such, we remain optimistic about future opportunities in China’s IDC industry and confident in our ability to seize them, owing to our established competitive advantages in the field. Going forward, we will remain focused on securing additional pipeline resources in key markets, upgrading our technology on a continual basis, and ensuring the reliability of our operations to provide customers with premium IDC services.”

Ms. Sharon Liu, Chief Financial Officer of the Company, commented, “With both our revenues and adjusted EBITDA meeting our previous guidance expectations, we delivered a solid quarterly financial performance to conclude 2019. In particular, we are pleased to have obtained additional capital as part of our three-year growth plan to fund those initiatives which will enable us to reach our development goals going forward. Looking into 2020, we will maintain our focus on expanding our cabinet capacity, ramping up our financial growth, and optimizing our operational efficiency. In addition, we will also continue to implement a prudent financial policy while closely monitoring the development of the COVID-19 epidemic.”

Fourth Quarter 2019 Financial Results

REVENUES: Net revenues in the fourth quarter of 2019 increased by 16.2% to RMB1.05 billion (US$150.6 million) from RMB901.9 million in the fourth quarter of 2018, representing an increase of 6.8% from RMB981.0 million in the third quarter of 2019. The year-over-year increase was primarily attributable to the growing demand for data centers in the domestic market, driven by the ongoing expansion of corporate digitization across China.

GROSS PROFIT: Gross profit in the fourth quarter of 2019 was RMB247.9 million (US$35.6 million), compared to RMB246.3 million in the same period of 2018 and RMB222.6 million in the third quarter of 2019. Gross margin in the fourth quarter of 2019 was 23.6%, compared to 27.3% in the same period of 2018 and 22.7% in the third quarter of 2019. The year-over-year decrease in gross margin was mainly due to the delivery of additional pipeline capacity.

ADJUSTED CASH GROSS PROFIT, which excludes depreciation, amortization, and share-based compensation expenses, increased by 4.1% to RMB425.9 million (US$61.2 million) in the fourth quarter of 2019 from RMB409.2 million in the fourth quarter of 2018, representing an increase of 7.3% from RMB396.7 million in the third quarter of 2019. Adjusted cash gross margin in the fourth quarter of 2019 was 40.6%, compared to 45.4% in the same period of 2018 and 40.4% in the third quarter of 2019.

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OPERATING EXPENSES: Total operating expenses in the fourth quarter of 2019 was RMB244.4 million (US$35.1 million), compared to RMB181.4 million in the fourth quarter of 2018 and RMB157.1 million in the third quarter of 2019. As a percentage of net revenues, total operating expenses increased to 23.3% in the fourth quarter of 2019 from 20.1% in the fourth quarter of 2018 and 16.0% in the third quarter of 2019.

Sales and marketing expenses in the fourth quarter of 2019 increased by 28.4% to RMB63.2 million (US$9.1 million) from RMB49.2 million in the fourth quarter of 2018, representing an increase of 20.6% from RMB52.4 million in the third quarter of 2019. The increase of sales and marketing expenses was mainly attributable to the Company’s business expansion efforts and the related increase in sales commissions to staff.

Research and development expenses in the fourth quarter of 2019 were RMB24.9 million (US$3.6 million), compared to RMB23.6 million in the same period of 2018 and RMB22.5 million in the third quarter of 2019.

General and administrative expenses in the fourth quarter of 2019 were RMB110.0 million (US$15.8 million), compared to RMB131.0 million in the same period of 2018 and RMB82.2 million in the third quarter of 2019. The year-over-year decrease was mainly attributable to the Company’s continuous efforts in maximizing its operating efficiency.

ADJUSTED OPERATING EXPENSES, which exclude share-based compensation expenses, changes in the fair value of contingent purchase consideration payables, and impairment of receivables from equity investees, increased by 6.8% to RMB184.2 million (US$26.5 million) in the fourth quarter of 2019 from RMB172.4 million in the fourth quarter of 2018, representing an increase of 26.0% from RMB146.2 million in the third quarter of 2019. As a percentage of net revenues, adjusted operating expenses reduced to 17.6% in the fourth quarter of 2019 from 19.1% in the fourth quarter of 2018 and increased from 14.9% in the third quarter of 2019.

ADJUSTED EBITDA: Adjusted EBITDA in the fourth quarter of 2019 increased by 3.3% to RMB263.8 million (US$37.9 million) from RMB255.3 million in the same period of 2018, representing a decrease of 3.2% from RMB272.5 million in the third quarter of 2019. Adjusted EBITDA in the fourth quarter of 2019 excluded share-based compensation expenses of RMB8.6 million (US$1.2 million). Adjusted EBITDA margin was 25.2% in the fourth quarter of 2019, compared to 28.3% in the same period of 2018 and 27.8% in the third quarter of 2019.

NET PROFIT/LOSS: Net loss attributable to ordinary shareholders in the fourth quarter of 2019 was RMB16.4 million (US$2.4 million), compared to a net loss of RMB114.1 million in the fourth quarter of 2018 and a net loss of RMB69.5 million in the third quarter of 2019. Net loss attributable to ordinary shareholders in the fourth quarter of 2019 included a foreign exchange gain of RMB22.5 million (US$3.2 million), compared to RMB2.5 million in the same period of 2018 and a foreign exchange loss of RMB40.2 million in the third quarter of 2019, and an interest expense of RMB88.4 million (US$12.7 million), compared to RMB72.4 million in the same period of 2018 and RMB96.9 million in the third quarter of 2019.

PROFIT/LOSS PER SHARE: Basic and diluted loss per share were RMB0.02 (US$0.3 cent) in the fourth quarter of 2019, which represents the equivalent of RMB0.12 (US$1.8 cent) per American Depositary Share (“ADS”). Each ADS represents six ordinary shares. Diluted loss per share is calculated using net loss attributable to ordinary shareholders divided by the weighted average number of diluted shares outstanding.

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As of December 31, 2019, the Company’s cash and cash equivalents, restricted cash, and short-term investments were RMB2.72 billion (US$390.9 million).

Net cash generated from operating activities in the fourth quarter of 2019 was RMB444.8 million (US$63.9 million), compared to RMB237.0 million in the same period of 2018 and RMB103.0 million in the third quarter of 2019.

Full Year 2019 Financial Results

REVENUES: Net revenues in the full year of 2019 increased by 11.4% to RMB3.79 billion (US$544.3 million) from RMB3.40 billion in the full year of 2018. The increase was primarily due to the same factors that led to the quarterly increase.

GROSS PROFIT: Gross profit in the full year of 2019 was RMB 939.4 million (US$134.9 million), compared to RMB944.9 million in the full year of 2018. Gross margin was 24.8% in the full year of 2019, compared to 27.8% in the full year of 2018.

ADJUSTED CASH GROSS PROFIT, which excludes depreciation, amortization, and share-based compensation expenses, increased by 8.0% to RMB1.63 billion (US$234.6 million) in the full year of 2019 from RMB1.51 billion in the full year of 2018. Adjusted cash gross margin in the full year of 2019 was 43.1%, compared to 44.5% in the full year of 2018.

OPERATING EXPENSES: Total operating expenses in the full year of 2019 increased by 7.0% to RMB757.2 million (US$108.8 million) from RMB707.4 million in the full year of 2018. As a percentage of net revenues, total operating expenses decreased to 20.0% in the full year of 2019 from 20.8% in the full year of 2018. The decrease of operating expenses as a percentage of net revenues was primarily due to the successful implementation of the Company’s efficiency enhancement initiatives.

Sales and marketing expenses in the full year of 2019 were RMB206.3 million (US$29.6 million), compared to RMB172.2 million in the full year of 2018.

Research and development expenses in the full year of 2019 were RMB88.8 million (US$12.8 million), compared to RMB92.1 million in the full year of 2018.

General and administrative expenses in the full year of 2019 were RMB415.3 million (US$59.7 million), compared to RMB462.6 million in the full year of 2018.

ADJUSTED OPERATING EXPENSES, which exclude share-based compensation expenses, changes in the fair value of contingent purchase consideration payables, and impairment of receivables from equity investees, decreased by 0.2% to RMB663.0 million (US$95.2 million) in the full year of 2019 from RMB664.4 million in the full year of 2018. As a percentage of net revenues, adjusted operating expenses decreased to 17.5% in the full year of 2019 from 19.5% in the full year of 2018.

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ADJUSTED EBITDA: Adjusted EBITDA in the full year of 2019 increased by 14.5% to RMB1.05 billion (US$150.9 million) from RMB917.7 million in the full year of 2018. Adjusted EBITDA in the full year of 2019 excluded share-based compensation expenses of RMB43.9 million (US$6.3 million). Adjusted EBITDA margin expanded to 27.7% in the full year of 2019 from 27.0% in the full year of 2018.

NET PROFIT/LOSS ATTRIBUTABLE TO ORDINARY SHAREHOLDERS: Net loss attributable to ordinary shareholders for 2019 was RMB182.3 million (US$26.2 million), compared to a net loss of RMB205.1 million in the full year of 2018. Net loss in the full year of 2019 included a foreign exchange loss of RMB28.0 million (US$4.0 million), compared to RMB81.1 million in the full year of 2018.

PROFIT/LOSS PER SHARE: Basic and diluted loss per share were RMB0.27 (US$0.04) for the full year of 2019, which represents the equivalent of RMB1.62 (US$0.24) per ADS. Diluted loss per share is calculated using net loss attributable to ordinary shareholders divided by the weighted average number of diluted shares outstanding.

Net cash generated from operating activities was RMB707.4 million (US$101.6 million) in the full year of 2019 compared to RMB705.0 million in the full year of 2018.

Recent Development

In February 2020, the Company announced that it had entered into convertible note purchase agreements with a group of investors led by Goldman Sachs Asia Strategic Pte. Ltd. for a total of US$200 million in convertible notes. These agreements are subject to the satisfaction of customary closing conditions. All convertible notes will mature in five years from the date of issuance.

Financial Outlook

For the first quarter of 2020, the Company expects net revenues to be in the range of RMB1,070 million to RMB1,090 million. Adjusted EBITDA is expected to be in the range of RMB245 million to RMB265 million.

For the full year of 2020, the Company expects net revenues to be in the range of RMB4,600 million to RMB4,800 million. Adjusted EBITDA is expected to be in the range of RMB1,250 million to RMB1,350 million. The midpoints of the Company’s updated estimates imply an increase of 24% year over year both in net revenues and adjusted EBITDA.

The forecast reflects the Company’s current and preliminary view on the market and its operational conditions, which do not factor in any of the potential future impacts caused by the COVID-19 epidemic and are subject to change.

Conference Call

The Company will hold a conference call at 8:00 P.M. on Wednesday, March 4, 2020, U.S. Eastern Time, or 9:00 A.M. on Thursday, March 5, 2020, Beijing Time, to discuss the financial results.

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Participants may access the call by dialing the following numbers:

The replay will be accessible through March 12, 2020, by dialing the following numbers:

A live and archived webcast of the conference call will be available through the Company’s investor relation website at http://ir.21vianet.com.

Non-GAAP Disclosure

In evaluating its business, 21Vianet considers and uses the following non-GAAP measures defined as non-GAAP financial measures by the SEC as a supplemental measure to review and assess its operating performance: adjusted cash gross profit, adjusted cash gross margin, adjusted operating expenses, adjusted EBITDA, adjusted EBITDA margin, The presentation of these non-GAAP financial measures is not intended to be considered in isolation or as a substitute for the financial information prepared and presented in accordance with U.S. GAAP. For more information on these non-GAAP financial measures, please see the table captioned “Reconciliations of GAAP and non-GAAP results” set forth at the end of this press release.

The non-GAAP financial measures are provided as additional information to help investors compare business trends among different reporting periods on a consistent basis and to enhance investors’ overall understanding of the Company’s current financial performance and prospects for the future. These non-GAAP financial measures should be considered in addition to results prepared in accordance with U.S. GAAP, but should not be considered a substitute for, or superior to, U.S. GAAP results. In addition, the Company’s calculation of the non-GAAP financial measures may be different from the calculation used by other companies, and therefore comparability may be limited.

Exchange Rate

This announcement contains translations of certain RMB amounts into U.S. dollars (“USD”) at specified rates solely for the convenience of the reader. Unless otherwise stated, all translations from RMB to USD were made at the rate of RMB6.9618 to US$1.00, the noon buying rate in effect on December 31, 2019, in the H.10 statistical release of the Federal Reserve Board. The Company makes no representation that the RMB or USD amounts referred could be converted into USD or RMB, as the case may be, at any particular rate or at all. For analytical presentation, all percentages are calculated using the numbers presented in the financial statements contained in this earnings release.

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Statement Regarding Unaudited Condensed Financial Information

The unaudited financial information set forth above is preliminary and subject to potential adjustments. Adjustments to the consolidated financial statements may be identified when audit work has been performed for the Company’s year-end audit, which could result in significant differences from this preliminary unaudited condensed financial information.

About 21Vianet

21Vianet Group, Inc. is a leading carrier- and cloud-neutral Internet data center services provider in China. 21Vianet provides hosting and related services, including IDC services, cloud services, and business VPN services to improve the reliability, security and speed of its customers’ Internet infrastructure. Customers may locate their servers and equipment in 21Vianet’s data centers and connect to China’s Internet backbone. 21Vianet operates in more than 30 cities throughout China, servicing a diversified and loyal base of nearly 5,000 hosting and related enterprise customers that span numerous industries ranging from Internet companies to government entities and blue-chip enterprises to small- to mid-sized enterprises.

Safe Harbor Statement

This announcement contains forward-looking statements. These forward-looking statements are made under the “safe harbor” provisions of the U.S. Private Securities Litigation Reform Act of 1995. These statements can be identified by terminology such as “will,” “expects,” “anticipates,” “future,” “intends,” “plans,” “believes,” “estimates” and similar statements. Among other things, quotations from management in this announcement as well as 21Vianet’s strategic and operational plans contain forward-looking statements. 21Vianet may also make written or oral forward-looking statements in its reports filed with, or furnished to, the U.S. Securities and Exchange Commission, in its annual reports to shareholders, in press releases and other written materials and in oral statements made by its officers, directors or employees to third parties. Statements that are not historical facts, including statements about 21Vianet’s beliefs and expectations, are forward-looking statements. Forward-looking statements involve inherent risks and uncertainties. A number of factors could cause actual results to differ materially from those contained in any forward-looking statement, including but not limited to the following: 21Vianet’s goals and strategies; 21Vianet’s expansion plans; the expected growth of the data center services market; expectations regarding demand for, and market acceptance of, 21Vianet’s services; 21Vianet’s expectations regarding keeping and strengthening its relationships with customers; 21Vianet’s plans to invest in research and development to enhance its solution and service offerings; and general economic and business conditions in the regions where 21Vianet provides solutions and services. Further information regarding these and other risks is included in 21Vianet’s reports filed with, or furnished to, the Securities and Exchange Commission. All information provided in this press release and in the attachments is as of the date of this press release, and 21Vianet undertakes no duty to update such information, except as required under applicable law.

Investor Relations Contacts:

21Vianet Group, Inc.

Rene Jiang

+86 10 8456 2121

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IR@21Vianet.com

Julia Jiang

+86 10 8456 2121

IR@21Vianet.com

ICR, Inc.

Xinran Rao

+1 (646) 405-4922

IR@21Vianet.com

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21VIANET GROUP, INC.

CONSOLIDATED BALANCE SHEETS

(Amount in thousands of Renminbi (“RMB”) and US dollars (“US$”))

21VIANET GROUP, INC.

CONSOLIDATED STATEMENTS OF OPERATIONS

(Amount in thousands of Renminbi (“RMB”) and US dollars (“US$”) except for number of shares and per share data)

21VIANET GROUP, INC.

RECONCILIATIONS OF GAAP AND NON-GAAP RESULTS

(Amount in thousands of Renminbi (“RMB”) and US dollars (“US$”))

21VIANET GROUP, INC.

CONDENSED CONSOLIDATED STATEMENT OF CASH FLOWS

(Amount in thousands of Renminbi (“RMB”) and US dollars (“US$”))