The competition is aimed at 16- to 24-year-olds, and offers the winner the chance to become the online "face" of 4Music, the pop music TV channel that is part of the Box TV network.
Vlogstar aims to find undiscovered vlogging talent in a four-week competition, which is entered by submitting a YouTube video to a 4Music and O2 branded Vlogstar hub.
The winner will go behind-the-scenes on 4Music shoots and gigs, and create one or two music-related video stories a week, an album or single review every week and a review of a music video every week.
O2 is promoting its new Big Bundles tariff, aimed at young adults that want to "live big" on a budget.
Kate Mulligan-Brown, the head of pay and go at O2, said: "As the UK's largest music channel, 4Music is the perfect fit, tapping into our customers' passion for music, celebrity and social media."
The O2 deal includes a ten-second teaser campaign for the competition across all Box TV channels except Magic, until 14 September. The brand will also receive bumper idents around 4Music shows such as' 4Music Requests' and 'Fresh Hits', until December.
The Vlogstar winner will also receive prizes including a Panasonic HD camcorder, a Samsung Galaxy and O2 Big Bundles SIM card.
Matt Rennie, the managing director of Box TV, said the way young audiences engage with media was evolving: "They're not just passively watching content, they're creators, reviewers and contributors too."
He added: "Forward-thinking brands like O2 know that to really engage with this audience they need to be part of that process, and with its social focus, the Vlogstar talent search provides the perfect platform for direct engagement."
4Music ran a similar 'Blogstar' competition in 2010 for bloggers, which had no commercial sponsor.