Russian finance company DST has also invested a further $50m (?32.2m) in the site.

The Washington Post reports, "The new valuation has added fuel to rumors circulating that Facebook may be under pressure to go public as the Securities and Exchange Commission prepares to launch an investigation into Facebook, Twitter, LinkedIn and Zynga stock trades."

Facebook was named by online metrics company Experian Hitwise as the most-viewed website in the US in 2010, overtaking Google for the first time. It ...