While 90% of 50 large retailers are active on Twitter, only 29% use the platform to actively engage with shoppers, according to a study by digital marketing firm Acquity Group. Acquity studied the 50 retailers included in consulting firm Interbrand’s report, “Best Retail Brands 2012.”

Even though fewer retailers are on the social networking sites Pinterest (60%) and Instagram (42%), most of the retailers that have a presence on these sites engage with shoppers there. 80% of the brands on Instagram are responding to consumers on the Facebook-owned social network and 70% of those on Pinterest are interacting with shoppers.

The report also found that 76% of the brands have established a presence and attracted followers on at least one of the following social networks: Facebook, Twitter, Instagram, Pinterest and YouTube.

“Although most brands are signed up for the major social networks, many struggle to understand how they fit into their overarching business strategy,” says Jay Dettling, executive vice president at Acquity.

That can be damaging because consumers may decide to buy from a different retailer after their messages are ignored, he says. “The important takeaway for brands is to avoid haphazard or sporadic use of social media,” he says. “When a new social media channel is introduced, brands need to take the time to analyze the potential impact and return, and develop a solid strategy from there.”

The study examined the 50 companies looking at quantitative metrics across a variety of channels, which also included in-store, standard web site, mobile, search and e-mail. Companies were awarded points based on their level of interaction with consumers across each of these channels and were further evaluated on a qualitative scale to assess consistency across marketing channels.

The brands leading the way in terms of social media, in order of score in the Acquity study, include: Target Corp., the Home Depot Inc., RadioShack Corp., Bath & Body Works, Nordstrom Inc., Gap Inc., eBay Inc., Coach Inc., American Eagle Outfitters Inc. and Gap Inc.’s Banana Republic. Target is No. 23 in the Internet Retailer Top 500; Home Depot is No.42, RadioShack No. 275, Nordstrom No. 31, Gap No. 22, Coach No. 158, American Eagle Outfitters No. 65.