Facebook Founder's Phantom Fortune Fizzles 9.47K Owen Thomas 03/11/09 06:10PM Filed to: Zuckerfreude Zuckerfreude Mark Zuckerberg Facebook Schadenfreude Valleywag Mark Zuckerberg owns 27 percent of Facebook. That's great, right? Except Facebook is not worth $15 billion anymore (if it ever was). That means he's no longer a paper billionaire, says Forbes.