Facebook shares continued to slide yesterday, amid ongoing furore concerning the use of data collected by the social network, BBC reports.
The firm's stock closed down 2.6%, following a steep decline a day earlier.
The concerns infected fellow social media company Twitter, which was down more than 10%.
Investors are reacting to calls for tighter regulation of tech firms from politicians in the US, UK and Europe.
On Tuesday, US media reported that the Federal Trade Commission, a US regulator, is looking into Facebook's handling of personal data.
The questions follow allegations that 50 million Facebook users' private information was misused by a political consultancy firm.
Cambridge Analytica (CA), used by the Trump campaign in the 2016 US election, has been accused of taking personal data without users' knowledge.
The firm's chief executive Alexander Nix has been suspended by the company's board.