CHICAGO (CBS) – Stores on the Mag Mile are on alert after several thefts involving flash mobs. In each case, a group of teens create a disturbance, steal items and then run from the stores.

CBS 2’s Suzanne Le Mignot reports in the past several weeks, there have been at least three incidents on Michigan Avenue. Sources tell CBS 2 the teens involved are between 17 and 13 years old.

Apparently they’ve been Tweeting each other. They pick a spot to meet and then go as groups to carry out their crimes. It’s all part of a growing phenomenon.

You can see mob robbery videos on YouTube. In one tape, 50 teens are seen entering a St. Paul, Minnesota convenience store. Within minutes they take whatever they want and leave. The same thing has been happening in Chicago along the Magnificent Mile. Sources said Filene’s Basement, The North Face store and Express have all been recent targets by these flash mobs.

“Just see kids, random kids running out of stores,” said witness Miralem Mahmatovic.

Mahmatovic said it’s been obvious the teens seen running, have had merchandise with them. He said he has seen a teen theft mob in action. “We had a cop from Express chase down a kid here once, just chased her, caught her down at the corner, so we’ve seen it a couple of times.”

At Express, sources said 11 teens stormed through the doors knocking over merchandise and alarming customers. Security tried to lock the doors and when police caught the teens, they also had merchandise with them from other stores.

Greater North Michigan Avenue Association President and CEO John Chikow said he organized a meeting Tuesday with law enforcement and representatives from about 70 stores along the Mag Mile. “The police gave a briefing as to what their current activities are. I think there’s a stronger commitment on the part of the businesses to call when there are problems because they’re seeing the police are responding very quickly,” Chikow said.

At Filene’s, teens ran onto the sales floor, grabbed items then ran out. At The North Face, they entered screaming and yelling, knocking over displays and grabbing clothes worth close to $3,000.

“We’re not gonna tolerate this in the district. We’re just not gonna tolerate it,” Chikow said.

Police have increased patrols and are also focusing in on areas identified as teen meeting points. The moment a large group is seen gathering in a known area, the teens are told they will be arrested for loitering and will be arrested if they don’t leave immediately.

The teens involved in the recent theft mob incidents have been charged with retail theft and reckless conduct. The North Face, Filene’s and Express, all had no comment.