Facebook owner Meta Platforms saw its stock market value plummet by more than $230bn (£169bn) on Thursday, in a record daily loss for a US company.
Its shares fell 26.4% after quarterly figures disappointed investors.
Meta also said Facebook’s daily active users (DAUs) fell for the first time in its 18-year history.
The crash in the company’s share price saw chief executive Mark Zuckerberg’s net worth plummet by $31 billion, according to the Bloomberg Billionaires Index.
The drop in Mr Zuckerberg’s personal fortune was equivalent to Estonia’s annual gross domestic product.
Even after this drop, Mr. Zuckerberg has an estimated net worth of nearly $90 billion, meaning he is still one of the richest people in the world.
It came after Meta revealed that Facebook’s DAUs fell to 1.929 billion in the three months to the end of December, from 1.930 billion in the previous quarter.
It was the first time that this measure of activity on the world’s largest social network had been reversed.
Meta also warned of slowing revenue growth amid competition from rival platforms such as TikTok and YouTube, while advertisers also cut spending.
Mr Zuckerberg said the company’s sales growth had been hurt as the public, especially younger users, left for rivals.
The company expects revenue of between $27 billion and $29 billion for the first quarter of this year, which is below analysts’ expectations.
Although the company has invested in video services to compete with TikTok, owned by Chinese tech giant ByteDance, it makes less money from these offerings than its traditional Facebook and Instagram.
It’s clear that Meta faces a whirlwind of different issues.
Last year, Apple introduced its App Tracking Transparency Policy.
It lets users choose whether or not they want to be tracked across the internet by companies like Meta, who can then sell that information to advertisers.
This is a major problem for Facebook because finding information about you and selling it to advertisers is exactly how it makes money.
Its quarterly results showed a decline in advertising revenue, partly for this reason.
Meta rivals like TikTok are also attracting a younger audience. And user growth has stagnated around the world.
Meta earns money through advertising. Yet the company’s name has been changed to mark a concept — the Metaverse — something that doesn’t yet exist and won’t for years.
Mark Zuckerberg has pledged to spend tens of billions of dollars on the project, even though evidence that people actually want to live their lives in virtual reality is scarce.
All of this means that many investors are not friends.
Meta, which owns the world’s second-largest digital advertising platform after Google, also said it was hit by privacy changes to Apple’s operating system.