The drop translates to a US$119.4 billion ($176 billion) decline in market capitalisation, the largest-ever loss of value in one day for a United States traded company.
Wehner added saying, "European ad revenue growth decelerated more quickly than other regions and was impacted primarily by reduced currency tailwinds and, to a lesser extent, the roll-out of GDPR".
"Over the next several years, we would anticipate that our operating margins will trend towards the mid-30s on a percentage basis", Wehner told the results conference call with analysts.
Zuckerberg and Facebook are being sued in what could be the first of many lawsuits over a disappointing earnings announcement by the social media company that wiped out billions of shareholder wealth yesterday.
The loss is the biggest one-day wipeout of individual wealth ever recorded on the ranking, which started tracking the world's biggest fortunes in 2012.
Shares in Alphabet were unchanged while those in Apple Inc and Netflix Inc dipped just a third of a percent. Investors also appear to have been alarmed by an alert from Facebook executives that revenue growth would slow as the company refocuses on improving user privacy.
Their median target price now sits at $219.30.
Rahul Shah, chief executive officer at Ideal Asset Management in NY, a Facebook shareholder, said executives were trying to reset expectations about growth but the outlook caught Wall Street by surprise.
"We own it for its leadership in the tech industry", he said.