Shoppers who land on retail sites through Facebook or Twitter are less likely to make purchases. Their conversion rates average 1.2 percent and 0.5 percent, respectively. Per average order, however, they spend more than those who come through Google. In fact, shoppers who originated from Twitter spend on average $121.33 — the highest average order value (AOV) of all, according to a recent study.

The RichRelevance study of more than 200 million shopping sessions provides insight into how Americans browse and shop online, and how their behavior varies, depending on whether they arrive at retail sites through social networks or search engines.

The National Retail Association reports that 37 percent of consumers plan to make online purchases this holiday season.

While Traffic from Twitter and Facebook to retail sites continues to grow dramatically, these networks still account for less than 1 percent of total traffic, according to Diane Kegley, RichRelevance’s CMO.

It may seem a bit odd that Twitter would produce the highest AOV, but when adding “intent” into the equation it makes sense. Consumers on Facebook and Twitter don’t intend to make a purchase, but rather share information. A spontaneous shopper might see an ad and get pulled into the retailer’s Web site. The shopper’s personality, combined with impulse and influence from the ad, prompts the sale or conversion.

Facebook continues to grow the most of any channel as a source of retail shopping traffic — contributing 92 percent more in August 2011, compared with the prior year.

The study also finds that organic search engine traffic remains a primary source for retailers, driving 18 percent of all traffic in August. Google accounts for the bulk — 81 percent of organic search traffic to major retailers. The surprise: AOL is identified as producing the highest conversion rate, slightly edging out Yahoo for highest AOV at $105.27. Although they spend more, only 1.7 percent of consumers arrive on retail sites from AOL. Yahoo and Bing account for 9.7 percent and 7.5 percent of traffic, respectively.

This AOL stat may also seem out of place until considering that the engine and portal represents one of the oldest among the group. In 2008, Saul Hansell at The New York Times ran a piece asking for help to identify who uses AOL and why. More than a decade ago, citing these numbers for the portal might have made a bigger splash, but it turns out the answer points to habit.

An older generation that might have more discretionary funds, tends to use the site. Retailers need to adapt to the way consumers will spend their share of the NFR estimated $450 billion in holiday online spending. That might mean wrapping e-commerce services around Facebook, Google, or direct email links.

Think of the data as a “wake-up call” to find new ways to reach and keep consumers satisfied, said Kegley. Also consider the drop in AOV from $128.27 to $116.58, for which RichRelevance attributes the decline to budgeting constraints and shipping costs that encourage smaller purchases.