Thursday's plunge knocked roughly $120 billion in market value off the tech stock and dragged the rest of the sector lower . Before Thursday, Facebook's largest single-day loss came in July 2012 when it shed 11 percent.

The shares fell as low as $173.75 Thursday before ending the session at $176.26.

Facebook just suffered its worst day as a public company, shedding 19 percent after a second-quarter revenue miss and disappointing daily active user count .

The company missed projections on key metrics after struggling with data leaks and fake news scandals.

European DAUs fell to 279 million from 282 million the previous quarter, potentially related to the effect of the enactment of the General Data Protection Regulation in the European Union. The set of regulations gives users more control over their online data.

North American DAUs remained flat despite the fallout from the Cambridge Analytica data leak scandal and fake news issues. However, average revenue per user in the region rose despite the lack of growth. It reached $25.91 per user, up from $23.59 in the first quarter.

Facebook also missed on advertising revenue projections, with $13.04 billion compared with the StreetAccount and FactSet estimate of $13.16 billion.

On a call with analysts, Facebook delivered some jarring warnings to investors, saying it expected its revenue growth rates to be lower than the year prior, especially in the second half of this year. (Facebook has a history of earnings calls that hurt the stock.)

At least three analysts downgraded the stock after the report, and many on Wall Street raised concerns about the company's policies and forecast.

As of Thursday's close, Facebook was flat on the year and up just 6 percent for the past 12 months. The stock is flirting with bear market territory — nearly 20 percent off its 52-week high — after having clawed its way back from those levels hit on the heels of the Cambridge Analytica privacy scandal earlier this year.