Scouring for secondhand clothes online is a more popular shopping tactic than ever before, according to a new report from resale site ThredUp . There are a half-dozen brands getting the most love on the online resale market these days, and they're mostly mall staples, per the site's fourth annual survey of the pre-owned shopping landscape.Old Navy is the top "value brand" and Ann Taylor is the most-desired "mainstream label" in terms of online resale, while Theory is nabbing the most attention among designer names on the resale market. J.Crew is the top "established resale brand," per the report, while Lululemon is the most sought-after "breakout resale brand." Though, interestingly, Lululemon ranked second in terms of most popular athletic brands, bested by Nike.Secondhand e-comm has apparently been booming in recent years, especially compared to other segments of the shopping community. The online apparel resale market has had an annual growth rate of 82% over past three years; e-comm had just 14%, and retail had a paltry 3%, according to the report, and the fashion resale market (online as well as brick-and-mortar) is expected to hit $25 million in 2025. While the retail market, on the whole, is projected to have an annual growth rate of 2% for the next decade or so, the resale market is slated to grow by 6% per year. (Granted, it's obviously in ThredUp's best interest to prove that there's a robust online resale market, but those kind of growth numbers are noteworthy nonetheless.)Are these the brands you're always on the hunt for when it comes to consignment shopping? Alternately, if you've got once-loved pieces languishing in your give-away pile, now might be the time to offload those neglected Lululemon leggings or an under-utilzed Theory blazer online...