The 19 per cent loss in Facebook's stock chopped $119 billion off its market value on Thursday.
It was the company's worst trading day since going public in 2012, and among the biggest one-day losses of market value in U.S. stock market history.
The loss came a day after Facebook revealed that its user base and revenue grew more slowly than expected in the second quarter as it grappled with privacy issues.
Those revelations stunned investors, who believed the company had weathered the recent scandal over users' privacy and pushed the stock to an all-time high Wednesday of $217.50.
The loss means in one day, just the decline in Facebook's market value is roughly the entire market value of McDonald's or Nike, give or take a few billion.
And it far exceeds to total market value of major U.S. multinational corporations such as General Electric, Eli Lilly or Caterpillar.
The company still has a total market value close to $511 billion, which exceeds the annual gross domestic product of countries like Poland, Belgium and Iran.
Facebook was downgraded by a number of industry analysts who were caught off guard by slowing growth in the wake of the Cambridge Analytica scandal.
- With files from The Associated Press