The move comes after WPP and LiveWorld formed a joint venture in July, with both firms saying they have seen growing demand for marketing services focusing on online communities.
LiveWorld has developed social networking applications such as blogs and messageboards for firms including MTV Latin America and eBay.
"In less than two months since announcing the LiveWorld-WPP joint venture, we have already closed new community marketing programs with major brands," said Mark Read, strategy director, WPP and CEO of wpp.com.
Other participants in the investment included Abundance Partners, several partners of Allegis Capital, a California-based venture capital firm with an existing position in LiveWorld, and several partners in the DragonBridge, a fund focused on the development of new business in China.
The move also follows WPP’s recent investment in online reputation monitoring firm Visible Technologies, whose CEO Adam Selig we interviewed earlier this month.
WPP also recently bought into video game advertising company WildTangent, and is expected to make more investments in the new media space later this year.