Forbes released its 2011 Billionaires List Wednesday, and social media website Facebook Inc. made perhaps the biggest splash.

Facebook placed six of its founders and investors on the list, four of whom are new to the roster. Co-founder and CEO Mark Zuckerberg came in at No. 52, with an estimated worth of $13.5 billion, up from No. 212 and $4 billion last year.

He joins other familiar technology names  such as Google Inc. founders Sergey Brin and Larry Page, who both came in at No. 24 with $19.8 billion. Groupon Inc. added Eric Lefkofsky, the company’s lead investor.

The 2011 list breaks the record for the total number of listees at 1,210 and combined wealth at $4.5 trillion.

One in three billionaires on the list is an American, according to Forbes, and the United States has 10 more billionaires than a year ago, but 56 fewer than at its 2008 peak. The country is adding new billionaires at a slower pace than China and Russia.

Top on the list is Mexican telecom mogul Carlos Slim Helu with $74 billion. Microsoft Corp. co-chair Bill Gates is the top American and No. 2 in the world with $56 billion. Warren Buffett, CEO of Berkshire Hathaway Inc., was No. 3 with $50 billion.