More than 200 million people worldwide access Facebook through their mobile devices, and people who do so are twice as active on Facebook than non-mobile users, the social network reports. And mobile/social apps like Foursquare and shopkick are catching on. It looks like mobile technology and social media may be a good match.

Tee shirt e-retailer Threadless, which creates shirts based on designs voted upon by Threadless community members, is seeking to capitalize on this trend by launching a mobile-optimized version of its Threadless.com site. The m-commerce site not only facilitates browsing, searching and buying, but also rating tees, sharing designs and blogging. The retailer’s products are driven by its community of customers, who create tee shirt designs for themselves and, if they like, for sale on the site. Customers can rate tee shirt designs. And they can share product pages via built-in links to various social networks.

Threadless is encouraging mobile shopping with a banner across the top of every page of the m-commerce site, which was built by technology provider Mobify. The banner reads: “We’re mobile now! Shop on your fancy phone and get 20% off.”

“The new mobile site allows us to better connect with our amazing community,” says Threadless CEO Thomas Ryan. “We’re particularly excited that users can score community-submitted designs from anywhere.”

Threadless says that having a mobile-optimized site in the face of increasing traffic from devices running the Apple Inc. iOS, Google Inc. Android and Research in Motion BlackBerry mobile operating systems will reduce bounce rates and speed page load times. A site visitor “bounces” when he arrives on a page on a site and then immediately leaves.