Social networking online provider Facebook doubled its revenues in the first half of 2011 to $US1.6 billion ($A1.5 billion), the Wall Street Journal reported on Thursday.

The paper cited what it called knowledgeable sources in reporting the figure for a company which, because it is unlisted, is not require to publish its figures.

But with some 750 million Facebook members worldwide, the online site has attracted major interest both from advertisers as well as from potential investors should the firm ever go public.

Market analysts say a stock market launch would be a mega-event, which could make Facebook worth $US50 billion to $US100 billion.