Although Passenger calls itself an “on-demand customer collaboration” company, it’s probably simpler and more accurate to call it what it is: A market research firm operating through private, white-label social networks.

Putting consumers in a controlled online environment, where they can nevertheless interact with each other, gives marketers and product analysts from companies like Coca-Cola and Disney, both Passenger clients, insight into what people think of their products.

Using online social networking tools is gaining credibility as a better way than traditional panel-based research to get the true opinions of consumers. The trend has helped Passenger increase its yearly revenue ten times over, according to publicly released figures, with a 100 percent customer retention rate.

The $8 million funding was provided by existing investors. StarVest Partners led the round, and was joined by Shelter Capital Partners and Steamboat Ventures. The Los Angeles, Calif. company has taken $20.5 million to date.