"Painful to watch" might be the understatement of the year, Zuck. Facebook shares tumbled to a new low on Friday, dropping below the $20 mark, meaning the stock had dropped below half its initial value of $38. Facebook shares sagged 6.3 percent as it put millions more up for sale; the day's drop personally cost Zuckerberg $600 million. His net worth is now down to $10.2 billion, according to Bloomberg. Zuckerberg admitted, according to a report, that he has anxiety over the company's lost value and that the stock decline has been "painful to watch."