Visits to Facebook have surged since the social networking site opened its doors to the general public last September, although its market share continues to lag behind that of MySpace, according to new data released on Monday.

The surge in traffic at Facebook comes amid continued interest in the site from numerous media companies. Facebook has been the subject of buy-out speculation since last year, when Yahoo was rumoured to be mulling a bid of more than $1bn for the company.

Facebook accounted for 0.84 per cent of all US web visits in April, according to new data from Hitwise, a company that tracks visits to popular websites. That was more than double the figure from September, when Facebook dropped a requirement that users have a valid email address from a university or high school to be able to join the site.

Facebook’s market share among the top 20 social networking sites was mostly unchanged in the same period, however, as News Corp’s MySpace continued to command a substantial lead.

MySpace, bought by News Corp in 2005 for $580m, accounted for nearly 80 per cent of visits to the top 20 social networking sites last month, while Facebook accounted for just over 11 per cent, roughly the same as September. Bebo rounded out the top three, accounting for just 1.3 per cent of visits to social networking sites last month, a figure unchanged from September, Hitwise said.

Facebook is this week expected to roll out new features designed to allow outside companies to develop services on Facebook web pages. The revamp comes as traditional media groups seek ways to access the young audience of social networking sites.

Mark Zuckerberg, Facebook’s founder, is admired by moguls including Rupert Murdoch, who invited the young executive to attend a recent meeting for top executives from News Corp’s various news divisions. However, media executives and bankers said Facebook’s owners were not interested in selling the site, and there is widespread speculation that Facebook might seek an initial public offering.