More than 80 per cent of the biggest US advertisers are now using Facebook to promote themselves, suggesting that corporate America is starting to embrace the social networking site as a mainstream advertising platform.

This marks a striking shift as large companies were initially hesitant to advertise on social networks, since users appeared resistant to advertising and there were fears that corporate logos might appear alongside offensive content.

However, Facebook, which now has 340m unique monthly visitors, says that 83 of the top 100 advertising spenders in the US, as ranked by AdAge, the research group, now use its site. This group includes Johnson & Johnson, Nike and AT&T.

“Every client wants to talk about Facebook,” said Ed Montes, US managing director of Havas Digital, whose clients include Sears, Expedia and Air France. “I haven't seen this kind of consistent fervour for a company since Google.”

Unlike previous big brand advertising on the web, the ads on Facebook are not splashy displays and banners but more discreet, blending into the overall site design. They typically invite users to engage with companies, directing them to pages and applications where they can become fans of the company and receive regular updates.

“Facebook is trying to build a platform where consumers and marketers can interact in innovative ways,” said Mr Montes.

Starbucks has more than 3.7m fans on its Facebook page, while Coca-Cola has more than 3.5m.

“If you look at people's profile pages, you'll see a lot of commercial activity even without advertising,” says Sheryl Sandberg, Facebook chief operating officer.

Facebook does not charge companies to have a fan page or an application. Nor does it plan to take a cut of the increased e-commerce taking place on its applications.

However, Ms Sandberg argues that the effectiveness of these free services is prompting the big brands to advertise. In the past year, more big advertisers have also begun to campaign on MySpace.