As Facebook's share price took another tumble last week, Mark Zuckerberg got knocked off a list of the world's ten richest techie billionaires. He temporarily lost $423 million of his personal, on-paper fortune last Thursday as the stock price fell due to reports that there are approximately 83 million fake accounts on Facebook, a fact likely to affect ad revenue.

Also, Facebook continues to be dogged by the issue of their mobile app, which still doesn't have ads on it, and which is now being used by about half the site's user base on the regular.

Anyway, Zuck's still rich, and he regained most of that virtual wealth on Friday, when the stock bounced back up to $21.09 from its low of $20.04 on Thursday. He owns 503.6 million shares of the stock, and he briefly fell behind fellow tech billionaire James Goodnight as the tech worlds 10th richest person.

[Bloomberg via IBTimes]