NEW YORK — Facebook faced a day of reckoning as its shares plunged Thursday in the company’s worst trading day since going public in 2012. It was among the biggest one-day losses of market value in U.S. stock market history.

The 19 percent drop in Facebook shares vaporized $119 billion of the company’s market value. CEO Mark Zuckerberg alone saw his net worth fall by roughly $16 billion as a result.

In a sign of just how bullish investor expectations had been running, though, the collapse merely returned Facebook shares to a level last seen in early May. At that point, the stock was still recovering from an earlier battering over a major privacy scandal.

Late Wednesday, Facebook warned that its revenue growth will slow down significantly for at least the remainder of the year and that expenses will continue to skyrocket.

The earnings covered the company’s first full quarter since the Cambridge Analytica privacy scandal erupted. But analysts attributed the user growth shortfall largely to European privacy rules that went into effect in May, not to the furor over the political consulting firm with ties to President Donald Trump, which improperly accessed the data of tens millions of Facebook users.

Shares closed down almost 19 percent, at $176.26.

The company earned $5.1 billion, or $1.74 per share, up 31 percent and above analysts’ estimates of $1.71.

But revenue — up 42 percent to $13.23 billion — was slightly below the $13.34 that Wall Street was expecting.

Facebook had 2.23 billion monthly users as of June 30, up 11 percent from a year earlier. Analysts were expecting 2.25 billion, according to FactSet.