The social networking company loses approximately US$150 billion ($219b) in market capitalisation in under two hours, Reuters has reported.
The company's founder and CEO Mark Zuckerberg is counting the cost of user disenchantment as his fortune tumbled by US$16.8 billion ($24.5 billion) in after-hours trading on Wednesday, US time.
Shares of the social media giant slid 20 per cent at 5.37pm in New York on disappointing results.
Bloomberg reports if that holds through Thursday's close, he will slide to sixth place from third on the Bloomberg
Billionaires Index. It would also wipe his US$13.7 billion ($20 billion) of gains for the year, leaving Zuckerberg with just less than US$70 billion ($102.2b).
The after-hours trading was on lower-than-expected revenue numbers from its second-quarter earnings report and disappointing forecasts for future growth and costs that rattled investors.
It raised worries the political and social backlash against the company is affecting the company's bottom line.