Mobile social networking startup MocoSpace raised a $4 million B round from existing investors General Catalyst, Bob Pittman’s Pilot Group and former eBay exec Michael Dearing. The previous A round was $3 million in January 2007.

MocoSpace is a mobile-only social network with two million members and serving one billion pageviews a month (from mobile phones). When we last wrote about MocoSpace in August, it had half as many members and pageviews. Strangely, MocoSpace does not connect its members to their friends on online social networks such as Facebook or MySpace. This silo mentality seems a throwback to the days when mobile apps didn’t need to talk to the Web. I guess the kids who use MocoSpace always have their cell phones with them anyway. CEO Justin Siegel explains why he is ignoring the big social networks:

At this point we’re not joining, but it’s not a “political” stance. Our CTO doesn’t believe it’s relevant to us at this point. We’ve talked about letting people import their profiles, but we’ve been able to grow at a nice clip without doing that.

Competitors in the increasingly crowded mobile social networking space include Aka Aki, Loopt, Mig33, Pelago, Twipster, Zannel, etc.