The new year will bring an experiment in group sales, more social networking tie-ins and a possible Groupon offering for Threadless.com, says Cam Balzer, vice president of marketing for the online retailer of customized T-shirts.

The retailer enters 2011 with the strong wind of social media at its back. Thanks in part to a promotion that encouraged customers and fans to share goofy photos of pets, the Facebook fan base of Threadless.com surpassed 200,000 during the holiday shopping season, Balzer says.

The pet picture promotion, along with a handful of others that also relied on user-generated content, marked the first time Threadless has created a marketing campaign that ties together social media and e-mail, he says. “We tweeted about the contest,” he says, referring to Twitter messages. “The people following on Twitter came to Facebook, and the people on e-mail came to Facebook. It was a real effort to tie social media into everything else.”

Threadless in 2011 will continue to run marketing campaigns that are similarly unified, he adds. Earlier this year, the retailer started to lean on Facebook for more customer service tasks.

The retailer also plans to tap into one of e-commerce’s hottest trends: group buying promotions. The idea generally works like this: An online retailer offers a product or product line for sale, and promises to honor the discounts if enough shoppers say they want to buy the product. Threadless will use a Facebook application developed by technology vendor Wildfire to run the group-buying effort, which will involve limited-time deals for products—for instance, a T-shirt from a line of shirts deemed popular by shoppers, who often are hipsters and other fans of pop culture and irony.  “It will be oriented toward acquiring new customers on Facebook and rewarding existing customers,” he says.

Threadless so far has shied away from discounts via daily-deal site Groupon because the online coupon retailer takes what Balzer calls a significant chunk of revenue from retailers. (Other sources say Groupon’s typical commission is 50% of the offer.) But Threadless could change its policy in 2011, in large part because of the growing reach and power of Groupon. “We want to reach their distribution lists, acquire new customers by tapping into their customer base,” he says.