Consumers shopping with their mobile devices accounted for 19% of Rue La La’s Thanksgiving Day sales, up from 2% a year ago. The flash-sale site’s comparable-store sales also were up 79% versus a year ago, the company says.

“You can’t use grandma’s PC to shop on Thanksgiving, so our customers whipped out their mobile devices to shop,” says Fiona Dias, executive vice president of strategy and marketing at GSI Commerce Inc., which operates RueLaLa, No. 103 on Internet Retailer’s Top 500 Guide. 

Rue La La has a designated m-commerce site and launched shopping applications for Apple iPhone and Android phones this year. The company said last month that 13% of sales currently come through mobile, and projects that mobile sales may account for 20% of total sales during 2011.

Dias says GSI saw mobile sales rise significantly among its e-retail client portfolio on Thursday. She says mobile accounted for 2% to 3% of sales on Thanksgiving Day, up from virtually zero a year ago. GSI’s e-retail clients include RadioShack, Toys ‘R’ Us and The Sports Authority.