The fortunes of Alibaba Group Holding Ltd.’s billionaire co-founders have more than tripled this year as the company prepares for an initial public offering.

Alibaba Chairman Jack Ma, 49, has a $12.5 billion net worth, up $8.9 billion year-to-date, according to the Bloomberg Billionaires Index. Joseph Tsai, the company’s executive vice chairman, controls a $4.8 billion fortune.

China’s biggest e-commerce company is valued at $168 billion, based on the average calculations of 12 analysts surveyed by Bloomberg News on April 17. The valuation gives Alibaba a bigger market capitalization than Facebook Inc. and about half that of Google Inc.

Ma “had the foresight by going into the e-commerce area,” Ronald Wan, chief China adviser at Asian Capital Holdings Ltd., said by phone from Hong Kong. “He’s a market leader. His reputation, business philosophy, and foresight have made him a successful businessman.”

Alibaba filed a prospectus yesterday with the U.S. Securities and Exchange Commission that looks to sell about a 12 percent stake, which would make the offering around $20 billion based on the estimated value. The filing has a $1 billion placeholder amount, which is used to calculate registration fees and will change. The offering, expected in the coming months, will probably make the company’s 28 partners and founders millionaires.

Yahoo Transaction

The Hangzhou-based company was valued at $40 billion after a September 2012 transaction in which Yahoo Inc. sold part of its stake back to Alibaba. Yahoo owns 22.6 percent of the company. Alibaba’s valuation rose to $153 billion in February, based on the average calculations of 10 financial-services companies, including Goldman Sachs Group Inc., Sanford C. Bernstein & Co. and Macquarie Group Ltd.

“Jack Ma is a very competitive individual,” said Anthony Cragg, a Singapore-based fund manager at Wells Fargo Asset Management, which oversees about $487 billion of investments. Alibaba’s “footprint is incredible. It’s a fairly easy job to convert that to other activities like Alipay and other financial services.”

Still, Cragg said plans for the share sale come at a time when the IPO market is “shaky.” His funds invested in Alibaba through Softbank Corp., a shareholder in Ma’s company.

Florence Shih, a spokeswoman for Alibaba, declined to comment on the wealth of Ma and Tsai.