WPP has made its second foray in a month into the social media space with the purchase of a stake in reputation monitoring company Visible Technologies.

The ad giant said it had agreed to buy a quarter of the Seattle-based firm and entered into an option to acquire a further 26%.

Visible Technologies, which employs 28 people in four US offices, monitors how brands are being perceived within social networking communities, generating just over US$0.5 million in revenues last year.

It has two products which track search engine results and blogs, and already works with WPP unit Burson-Marsteller on its clients’ online PR.

The investment should fit nicely with WPP’s announcement last month of a joint venture with Liveworld which will aim to promote its clients within online communities.

It’s also significant in light of expectations that WPP boss Sir Martin Sorrell will paint a gloomy picture of the UK’s ad market on Friday.

What’s clear is that WPP realises consumers will continue to move away from traditional media, whether ad buyers like it or not.