According to figures from Media Metrix, Piczo has 10m unique users every month worldwide, with 4m teenagers in the UK visiting in July.
Piczo, which was founded in 2004, said it was encouraged by its viral UK growth, with Nielsen//NetRatings recording a 9,669% increase in website audience for 2005 -- making it the number-one brand for audience growth that year.
Jeremy Verba, CEO of Piczo, said: "While Piczo's success to date has been built predominantly on word of mouth, today's announcement signals a step change for us.
"We aim to expand our existing advertising and marketing relationships, and establish our presence in the UK with the appointment of an experienced senior management team."
Piczo, which targets 13- to 16-year-olds, provides personalised websites where registered users can upload pictures, music, text and graphics.
The company said it offered a more secure environment for teens to meet people online by adopting a "walled garden" approach to membership, by not having a user search function and leaving it up to individual members to decide with whom they wished to correspond.
Verba added: "Piczo is offering advertisers, such as film and music distributors, a range of solutions to the challenge of engaging this traditionally hard to reach segment."
Despite Piczo's strong growth over the last 12 months, it faces stiff competition from Rupert Murdoch's , which claims to have more than 100m registered users worldwide, and Bebo, which has reportedly attracted a bid from US media group Viacom.
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