On the company page of Rootsgear’s, which designs T-shirts with political and social messages, people can look at the firm’s designs and see a calendar of upcoming events. The company stokes its group membership of about 1,400 by every few months sending out invitations to join to new Facebook friends collected by cofounder Sunmit Singh. Mr. Singh says the Facebook page drives more traffic to Rootsgear’s e-commerce site than Google’s search engine or MySpace, another social-networking site where it has a presence. And Facebook has helped the year-old company’s sales.