Facebook now has one billion users, the equivalent of about one in seven of the world's population, its founder announced yesterday.

Mark Zuckerberg welcomed the "amazing, humbling" milestone, which has come in a year that has seen the social network float on the stock market to a mixed reaction.

More than $50 billion (£31.2bn) has been lopped off Facebook's market value as the company's share price has fallen from $38 when stocks were initially offered in May to yesterday's closing price of $21.94.

Mr Zuckerberg's own Facebook holdings have plummeted roughly more than $9bn as sceptics question his ability to lead the company.