Talk about having some wealthy friends. Six people involved with Facebook made Forbes magazine's 2011 Billionaires List.

Facebook co-founder Mark Zuckerberg is at the top of the richest social networkers with an estimated $13.5bn, according to Forbes. Zuckerberg had a good financial year, with his wealth jumping 238 percent in just the past year.

And Zuckerberg isn't alone. Company cofounders Dustin Moskovitz, Eduardo Saverin and Sean Parker also made Forbes' billionaire list.

Moskovitz, the world's youngest billionaire, was Zuckerberg's Harvard roommate and Facebook's third employee. Today, he's worth $2.7bn.

And Saverin, who started Facebook with Zuckerberg while they were in college, had a falling out with Zuckerberg - there was a lawsuit and counter-suit involved. The parties settled and Saverin now is worth $1.6bn.

As for Parker, the former Facebook president and co-founder of Napster also is worth $1.6bn.

Rounding out Facebook's billionaires are Peter Thiel, co-founder of PayPal and a Facebook investor, is worth $1.5bn, while Yuri Milner, who has invested in Facebook, Groupon and Zynga, is worth $1bn, according to Forbes.

Lest the folks at Facebook think they have a lock on all the social networking billionaires, Groupon and Zynga added a few names of their own to the Forbes list.

Mark Pincus, who founded social gaming company Zynga, is worth $1bn; and Eric Lefkofsky, co-founder of online discount provider Groupon, is reported to be worth $1.6bn.