Its criteria for representing publishers is they must have more than a million monthly UK unique users, a unique proposition and market-leading heritage in their category, and the desire to evolve their platform to meet advertiser demand.
The company was founded by JP Kemp, a former sales director of digital ad network Gorilla Nation and head of agency sales at Handbag Group, and Tom Barham, former deputy sales director of Gorilla Nation.
Kemp said the company would focus on "delivering great levels of service" to fewer publisher clients, and would attempt to carve out a niche away from the normal breed of sales houses that tend to represent more than 35 publishers.
Justin.tv allows people to create live video content and show it to anyone in the world, and appeals predominantly to young men.
The Student Room is a community for GCSE, A-Level and university students.
Claudine Love, commercial director of The Student Room, said: "SunChaser are giving us a voice at agency level that we would never have achieved using a traditional network.
"Whereas previously we saw a trickle of ROS media buys, we are now working closely with great brands such as Orange, Apple, Kelloggs and Barclays, to drive long-term dialogue with our audience, using a custom approach every time."