Other recent mob actions downtown include one in April, when a group of about 70 youths stormed a McDonald's restaurant at State Street and Chicago Avenue and created a disturbance. The restaurant was closed for nearly three hours.

In February, Loyola University Chicago warned its Water Tower campus students and staffers about "flash mob offenders" who would exit from Chicago Avenue's CTA Red Line station and allegedly steal items from retail stores around the campus.

Although there were reports of violent disturbances on North Avenue Beach on Memorial Day, acting police Superintendent Garry McCarthy told reporters later in the week that the beach was closed early because overcrowding made it difficult for ambulances to respond to people on the beach suffering from heat exhaustion.

Saturday's attacks happened in the Near North Police District, which includes areas of downtown such as Streeterville, the Gold Coast and the Magnificent Mile.

Crime statistics for those particular portions of the district weren't immediately available. But districtwide numbers show there were 141 robberies between January and the end of April, compared with 128 during the same time period the year before.

Although police have said retail theft was down by nearly 2 percent in the district between January and the end of April, there was an increase of at least 10 percent in juvenile shoplifting arrests.

Police and merchants stepped up security efforts after a rash of youth shoplifting incidents in February, said John Chikow, president of the Greater North Michigan Avenue Association. Chikow said police and individual merchants are monitoring social networking sites, the lines of communication apparently used by some teens to coordinate mobs.

"The best indicator that the police are doing their job and the community is reporting the incidents is an uptick (in arrests)," Chikow said.

From inside his newsstand on the corner of Chicago and Michigan, Jignesh Moodi said he has watched teen shoplifters apparently coordinating group assaults on stores via cellphone.

"They're on their phones and you see one outside say, 'Go!' and the ones inside grab stuff and run out," Moodi said. "They try to run up and take my magazines."

Pausing from passing out fliers for a discount men's store in the 400 block of North Michigan on Sunday, Joseph Reyes recalled being roughed up by a mob of about a dozen teens in October while he was wearing a gorilla suit to promote a Halloween store. Similar groups tried to shoplift from the store, prompting owners to hire private security.

"I'm from a bad neighborhood, and these kids are from some messed-up neighborhoods," Reyes said. "This is the best part of the city. This is our bread and butter. Why would you want to mess that up?"

Skyes, Pickett and Wright are scheduled to appear in bond court later Monday.

Tribune reporters Andrew L. Wang and Caroline Kyungae Smith contributed.

jgorner@tribune.com and agrimm@tribune.com