Facebook's stock plunge is deemed the biggest single-day loss in terms of individual stock in history.
Shares closed down almost 19% at $176.26, wiping more than $120 billion off the company's value or nearly four times the entire market capitalisation of Twitter.
The lawsuit is designed for class-action status and seeks unspecified damages.
The company also said revenue growth from emerging markets and the company's Instagram app, which has been less affected by privacy concerns, would not be enough to fix the damage.
Facebook warns privacy push will erode profits for years
This is not the first time the social media company has faced lawsuits this year with the company dealing with the aftermath of the Cambridge Analytica scandal. Since then, many have been consolidated in the federal court in San Francisco.
Kacouris said the marketplace was "shocked" when "the truth" began to emerge on Wednesday from the Menlo Park, California-based company. He also claims the massive plunge stemmed from "federal securities law violations from the defendants".
The company has reported dismal earnings, which seem to show that Facebook's growth is stagnating.
Mr Buffett now ranks third among the world's billionaires, while Mr Zuckerberg is sixth.
Liverpool players on the move
Jose Mourinho is adamant it is only right that people demand Liverpool win the Premier League as he mocked Jurgen Klopp's sudden enthusiasm for spending heavily in the transfer market.
Facebook founder, chairman and CEO Mark Zuckerberg, who has started feeling the pressure with lawsuits being filed against him, is also being asked to quit the top post by shareholders.
The revelation of a massive data leak in March was another factor that hurt the USA social networking giant.
Overnight, Wall Street's major indexes have closed lower as weak earnings reports from major technology companies led to a big drop for the sector.
"We own it for its leadership in the tech industry", he said.
GOP House Members Move To Impeach Deputy Attorney General Rod Rosenstein
Meadows and Jordan could still force the issue on Thursday before lawmakers head home for the House's month-long August recess. Minutes later, House Republicans voted to sanction the Department of Justice over GOP document requests.
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.
Facebook shares fell another 0.8 percent on Friday, closing at $174.89 on the Nasdaq.
Cyclists hit with spray as Tour halted by protests
As the Tour reached the mountains of the Pyrenees, Philippe Gilbert and Alaphilippe led on the ascent to Col de Portet-d'Aspet. The only thing lacking from the wild 16th stage of the Tour de France on Tuesday was a shakeup in the overall standings.