The Facebook brief is understood to be comprehensive, incorporating consumer, trade, corporate and crisis management work.
The website has brought in a UK-based intermediary to help find the right PR firm for the work, which is believed to be worth a six-figure sum.
Facebook's senior corporate comms manager Matt Hicks would only say that Facebook's focus is on "company growth". California-based Hicks did not deny having approached the 12 agencies but insisted that Facebook is "not at a point where we have anything official to report on the UK".
The website has enjoyed a meteoric rise in its profile since its US launch in early 2004, when Harvard University student Mark Zuckerberg opened the site to the Boston area and Ivy League students. It is now thought to be worth in excess of $10bn.
London has emerged as the Facebook capital of the world, with more active members than any other city, having overtaken Toronto last month. Tech PR insiders agreed that the account is one of the most sought after pieces of business to emerge this year.
However, Gareth Thomas, head of new media at Brands2Life, warned that the winning agency is likely to face a backlash.
"Facebook has had a pretty smooth ride so far, with the media generally falling over themselves to write any positive story about it," Thomas said. "But like anything hugely popular, it's not long before the backlash begins.
"We've seen this already with many workplaces banning Facebook, the voicing of privacy fears, and people getting annoyed with advertising and the constant spam of new applications. Beating the backlash will be Facebook's big PR challenge."