He was listed Thursday as $81.9 billion poorer than Jeff Bezos, who still hold the top spot on that list. It would also wipe his US$13.7 billion of gains for the year, leaving him with just less than US$70 billion.
What drove the selloff: Investor concern about Facebook's growth cooling down.
A total of $128 billion was wiped off Facebook's value in just two hours following the second quarter briefing, the first since the Cambridge Analytica scandal and new European Union data rules came into effect. Those problems hadn't mattered to the success of the business - until now.
As for Facebook, it actually made money in the quarter, just not enough to appease Wall Street.
"We plan to grow and promote certain engaging experiences like Stories that now have lower levels of monetization, and we are also giving people who use our services more choices around data privacy, which may have an impact on our revenue growth", said CFO David Wehner. "We're starting to see that this quarter", he said.
RBC Capital Markets analyst Mark Mahaney said the drop creates a rare buying opportunity for Facebook shares.
Until Wednesday, Facebook shares had been at record highs as investors seemed to shrug off fears about data protection and probes into the hijacking of private information by the political consultancy Cambridge Analytica.
At least 16 brokerages cut their price targets on Facebook after managers said the cost of improving privacy safeguards, as well as slowing usage in the biggest advertising markets, would hit the company's profit margins for more than two years. And the increased spending aims, among other things, to prevent a replay of the fake news and propaganda that Russian agents unleashed on an unguarded Facebook in an attempt to sway the 2016 presidential election.
Facebook's shares collapsed by 18% on Thursday when the stock market opened in NY, a day after the Silicon Valley company revealed that 3 million users in Europe have abandoned the social network since the Observer revealed the Cambridge Analytica breach of 87m Facebook profiles and the introduction of strict European Union data protection legislation. Though Facebook-specific global DAU rates were up 11 percent year over year - with growth led through users in India, Indonesia and the Philippines - it was less than Wall Street was projecting.
Total net sales for the second quarter rose 39 percent to $52.9 billion, missing the average analyst estimate of $53.4 billion. Analysts were expecting $2.1 billion, according to Thomson Reuters. The set of regulations gives users more control over their online data. And investors responded Thursday by hammering the stock of Facebook, one of the world's most valuable companies.
"Our total revenue growth rate decelerated approximately 7 percentage points in Q2 compared to Q1", he said. "Deceleration such as management guided toward suggests that while the company is still growing at a fast clip, the days of 30%+ growth are numbered".
"T$3 he number of daily active users on the platform - an important metric for judging the success of a website or app - only grew by 22 million - the lowest growth figure since 2011", Breitbart News divulged.
Some shareholders are saying Zuckerberg has gripped too much power at the company.
Zuckerberg placed himself in the midst of yet another controversy after he received considerable backlash for justifying the lack of diligence Facebook demonstrated while handling offensive social media content posted by Holocaust deniers. The company owns three other properties with more than 1 billion users: WhatsApp, Messenger and Instagram. It reached $25.91 per user, up from $23.59 during the first quarter. "Real world issues that people thought should affect the company are now affecting the company". He said the 19 percent plunge in Facebook shares the next day stemmed from federal securities law violations by the defendants.