Frances Haugen, a 37-year-old former product manager turned whistleblower, heavily criticised the company at a hearing on Capitol Hill.
Facebook however said Ms Haugen spoke about areas she has no knowledge of.
It comes amid growing scrutiny of the social media giant and increasing calls for its regulation.
Facebook is the world's most popular social media site. The company says it has 2.7 billion monthly active users. Hundreds of millions of people also use the company's other products, including WhatsApp and Instagram.