Four new radio companies will contribute inventory to TargetSpot, the largest online radio ad network, and its network of more than 75 terrestrial and online radio partners. The radio companies, Tribune Broadcasting, Emmis Radio, Lincoln Financial Media, and ICBC Holdings increase TargetSpot's monthly reach from 15 to more than 17 million listeners.

Radio broadcasters are looking to TargetSpot to help cultivate a lucrative revenue stream that could offset significant revenue declines. Internet radio has been a bright spot for the business, up 14 percent to $126 million in third quarter, per the Radio Advertising Bureau. According to eMarketer, Internet radio advertising is forecast to hit $394 million by 2011, making the segment one of the fastest-growing media segments.

"As a traditional broadcaster, it is important for us to align with a partner that is well-versed in the online space. TargetSpot's advertising network is designed to bring the most value to online audio and, in working with them, we're better positioned to grow digital revenue," said Keisha Sutton-James, VP of ICBC.

In September, TargetSpot added increased targetability to its service with the launch of TargetSpot Analytics. The new tracking and reporting system follows listeners' responses to ads from the time the spot aired through subsequent Internet activity.