Zuckerberg, according to the Bloomberg Billionaires Index, now trails only Amazon founder Jeff Bezos and Microsoft Corp co-founder Bill Gates as Facebook shares climbed 2.4 per cent.
The stock has spiked about 15% this year.
For the first time, the three richest people on the ranking made their fortunes in the tech world.
Zuckerberg, 34, is now worth $81.6 billion, about $373 million more than Buffett, the 87-year-old chairman and chief executive officer of Berkshire Hathaway Inc.
Facebook, since going public in 2012, had seen its stock rise more than 400 per cent.
Buffet gives billions of dollars to charity every year, since 2006. He’s donated about 290 million Berkshire Hathaway Class B shares to charities. Zuckerberg has pledged to give away 99 percent of his Facebook stock in his lifetime.