Social media monitoring firm Visible Technologies has received another round of funding, including the sale of a sizable stake to WPP Group, reports Adweek.

WPP Group first invested in Visible a year ago. This closer relationship brings the firm's investment in Visible to about US$9 million.

10 WPP-owned agencies currently use Visible's monitoring product, which scans social networks, blogs and other social media outlets for brand name mentions.

The Visible investment is only one area in which WPP has taken a stake in the social media world. The agency holding company also put money into ad network VideoEgg, social network creator LiveWorld and others.

WPP plans on investing in a number of such firms over the next year and a half.