The market capitalization of the social-networking giant was down by as much as $148 billion before recovering a bit later in the day.
The slower growth comes as the company grappled with privacy scandals.
Windsor added that Facebook is forced to hire more people to handle tasks such as filtering inappropriate content after discovering the limits of artificial intelligence. Brian Wieser of Pivotal Research, who rates Facebook shares a Sell, said the second quarter proves that the brakes are being pumped.
The plunge came one day after the firm missed revenue forecasts for the second quarter and warned that growth would be far weaker than previously estimated. One of the largest falls in stock market history.
Facebook reported a 42 percent increase in revenue and a 31 percent jump in profits for its second quarter, compared with a year earlier.
"Looking beyond 2018, we anticipate that total expense growth will exceed revenue growth in 2019", he said.
Yet Facebook is hardly a stranger to a volatile stock price and has rebounded from previous mishaps, including Cambridge Analytica. Within minutes it was down 15%, then 18%, then 24%. Facebook's market cap was $629 billion at market close Wednesday, and ended the day Thursday at around $510 billion.
In the Facebook stock sell-off, Zuckerberg lost almost $16 billion in personal wealth and some shareholders believe it's time the 34-year-old lost even more: his job. "In the USA and Canada, Facebook's daily active users remained flat sequentially at 185 million, while the number actually fell in Europe, falling to 279 million, down from 282 million", writes Fox News.
National Religious Broadcasters President Jerry Johnson told CBN News in an April interview that Facebook should apply the First Amendment to questions of speech; otherwise, he fears Christian and conservative voices will be silenced. Its overseas revenue got a boost in dollar terms as the dollar appreciated against other currencies a year ago.
Facebook didn't respond to a request for comment.
Gene Munster, a venture capitalist at Loup Ventures, said in an email that Facebook is "entering a new period" where declining user growth will translate to slower revenue growth.
At the same time, the company also reported that growth was flat in North America.
Wehner warned analysts not to expect the company's financial results to get better anytime soon.
"We own it for its leadership in the tech industry", he said.
As for Facebook, it actually made money in the quarter, just not enough to appease Wall Street.