(Reuters) - OnTheMarket, the online property portal challenging Zoopla and Rightmove (>> Rightmove Group), is looking to raise about 50 million pounds ($66 million) via a listing on London's junior market, its parent company said.

Agents' Mutual, a company launched and backed by estate agents, said OnTheMarket would seek a valuation of between 200 million and 250 million pounds via an initial public offering on the Alternative Investment Market.

It plans to offer investors a minority stake and to use the proceeds to attract and retain more estate agents via a national media campaign.

The group's existing members will vote on September 6 on the potential conversion of their interest in the portal into shares, so that the IPO can proceed, Agents' Mutual said.

OnTheMarket, currently the third biggest player in the UK residential property portals market, was launched in 2015 to challenge Zoopla Property Group (>> ZPG PLC) and Rightmove in the British online property search market.

It has about 2,700 estate and lettings agency firms as members, including Savills (>> Savills plc) and Knight Frank.

(Reporting by Esha Vaish in Bengaluru; editing by Jason Neely)

Stocks treated in this article : Savills plc, Rightmove Group, ZPG PLC