Armed with $20 bills, a group of about 60 shoppers descended on the Droolin' Moose in Burnsville on a frosty evening in late January -- normally a very slow time for the gourmet chocolate shop.

They came, they sampled, they bought chocolate treats packed into plastic cups bearing the Droolin' Moose signature cartoon logo. For many, it was the first time they'd been inside the small store tucked into the strip mall off County Road 42.

"It was super cool to watch people discover our store," said Missy Wettstrom, who designed the logo and owns the shop with her sister, Amy Bustos.

The Droolin' Moose was the latest target of Cash Mob South of the River, a loosely knit group of boosters that uses social media to rally support for independent local merchants. Using a Facebook page set up by its founders, the group chooses one small south metro business each month to "mob," arriving at a prearranged date and time with a goal of spending at least $20 each.

Cash mobs are a twist on flash mobs, brief events where people gather in public spaces for choreographed dance routines.

Cash mobs have been around for a couple of years and are believed to have gotten started in Buffalo, N.Y., where a group used Facebook and Twitter to rev up sales for local stores and restaurants.

Fueled by consumers' interest in buying local, the cash mob movement has spread to dozens of cities across the country, including Minneapolis and St. Paul.

Cash Mob South of the River was formed last summer by Matthew Johnson of Prior Lake and Ryan Berkness of Savage, who knew each other through a south metro area business networking group. The cash mob was a natural outgrowth of their full-time jobs: Johnson works for a business that operates customer loyalty programs for merchants, and Berkness operates a marketing firm that advises small businesses on using social media.

After coming up with the name and setting up the Facebook page, Johnson and Berkness used contacts in their networking group to spread the word about the new cash mob.

"It kind of grew on its own," Berkness said. "We really didn't think there would be much of a following, but apparently there's this very dedicated buy-local movement here that we just sort of stumbled on." Berkness said the cash mob's Facebook page has 850 "likes" and the group's e-mail list has a few hundred names.

The group chooses one merchant a month to mob, taking nominations on the Facebook page and letting people vote for a week or two. The winner, which frequently finds out through its own Facebook page that it's in the running, is contacted in advance so it can prepare for the rush of business. Johnson said the mob generally has its events on Thursdays around 5 p.m. to make it convenient for people to stop in on their way home from work.

The group suggests that folks spend around $20 and asks that they bring cash. Berkness said he wound up spending around $80 at the Droolin' Moose. "This is a business I'd never heard of before. That's part of the beauty of it," he said.

Wettstrom agreed. "The awareness that this creates is the biggest thing. The 850 likes on that Facebook page -- a lot of those are people who might not have even known about our business," she said.

Wettstrom also said the timing of the mob's visit may prove to be especially beneficial, since it was just a few weeks before the big candy-buying holiday of Valentine's Day.

"We normally have a lull in business in January, and anytime you can get an event right before a holiday it's never a bad thing," she said. One hopeful sign so far is a recent increase in the number of followers on the store's Facebook page, she said.

The group's other events have taken place at Junior's Sports Cafe, the Ficus & Fig gift shop, Ernie's Pub & Grille and Byblos Lebanese Grill in Burnsville, and Ansari's Mediterranean Grill & Lounge in Eagan.

The December outing at the Eagan restaurant proved to be a test of the cash mob's resolve, according to owner David Ansari.

"It was one of the first days that we had a real snowfall. The roads were pretty bad when I came into work, and we were thinking nobody was going to come," Ansari said. "It ended up being a full house. We were pleasantly surprised."

Ansari said he wasn't familiar with cash mobs before his restaurant had one, but has come to firmly support the concept.

He said it has also made him more aware of other local businesses, including the Droolin' Moose. "I plan on stopping over there and giving them some business, too."

Susan Feyder • 952-746-3282