Facebook founder Mark Zuckerberg has pledged to donate at least half his wealth to charity.
Mr Zuckerberg and Facebook co-founder Dustin Moskovitz have joined The Giving Pledge, a philanthropic campaign led by Warren Buffett and Bill Gates.
A total of 57 billionaires now have joined initiative, which was launched in June.
Mr Gates, his wife Melinda, and Mr Buffett have asked US billionaires to give away at least half their wealth during their lifetime or after their death, and to publicly state their intention with a letter explaining their decision.
The Giving Pledge does not accept money or tell people how to donate their money but asks billionaires to make a moral commitment to give their fortunes to charity.
"People wait until late in their career to give back. But why wait when there is so much to be done?" Mr Zuckerberg, who gave $100 million in September to the beleaguered public schools of Newark, New Jersey, said in a statement.
"With a generation of younger folks who have thrived on the success of their companies, there is a big opportunity for many of us to give back earlier in our lifetime and see the impact of our philanthropic efforts," he said.
In addition to the founders of Facebook, the world's youngest billionaires, pledges were made by AOL co-founder Steve Case, financier Carl Icahn and Michael Milken, a former Wall Street executive who went to prison in the early 1990s for securities violations.
Morningstar chief executive Joe Mansueto, businessman Nicolas Berggruen and private investor Ted Forstmann also are among the new billionaires to take the pledges.
"In just a few short months we've made good progress," said Mr Buffett, who made his fortune with insurance and investment company Berkshire Hathaway Inc.
"The Giving Pledge has re-energised people thinking about philanthropy and doing things in philanthropy and I look forward to many more conversations with families who are truly fortunate and whose generosity can and will change lives," he said.
The full list of billionaires and their letters can be seen at www.thegivingpledge.org.