Facebook has opened in US markets at a loss of 18.4 per cent, wiping roughly $123bn (£93.8bn) off its market valuation.
Discussed in an earnings call late last night, Facebook experienced zero growth in user numbers across North America, and actually lost users in Europe by about 1m. In after-hours trading, its share price fell as low as 24 per cent.
The social media giant revealed in its second quarter results that its monthly active user numbers across all of its platforms had grown to 2.23bn at an increase of just 11 per cent, falling short of consensus estimates of 2.25bn as polled by Thomson Reuters.
Those numbers are not just for its main Facebook site, but also across apps like Instagram and Whatsapp which are expected to have been behind the majority of the company's user growth.
As a result of the implementation of the General Data Protection Regulation, coupled with a hit from the Cambridge Analytica scandal, its CEO Mark Zuckerberg said the company is "investing so much in security that it will significantly impact our profitability".
This was evident in a 50 per cent rise in costs year-on-year for the quarter.
"The guidance from management over their expectations for revenue growth to decelerate so markedly for the rest of the year did take us, and the market, by surprise," said Christopher Rossbach, chief investment officer at J. Stern & Co.
"The share price decline of 20 per cent after hours is relatively understandable given the strong run over the last couple of months, and indeed over the last five years."
He added that it is "probably unlikely" that Facebook's share price will recover quickly, due to a resetting of expectations that will take time for investors to digest.
As a comparison, Facebook's market value loss of $123.4bn is more than seven times the valuation of Snap ($17bn), and almost four times the valuation of Twitter ($33bn).
Had Facebook opened as low as it had fallen last night, it would have marked the biggest fall after an earnings release in history.