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One adult and 11 juveniles were arrested Saturday after dozens of youths gathered in the city's Gold Coast, blocking traffic and causing other disturbances.
Police responded to reports early Saturday evening that a group of between 40 and 60 teens had gathered and were running around the Magnificent Mile shopping area on Michigan Avenue near the Chicago CTA Red Line stop, according to NBC Chicago.
One witness described the scene to ABC Chicago as "like a huge riot going on - someone held up a phone and the police knocked it out of her hand - that's all i saw, though. I'm scared for my safety."
Police arrested twelve in the group for causing what they've deemed a "minor disturbance." No injuries or other violence were reported, the Chicago Tribune reports.
The Saturday night disturbances came the same day that Gov. Pat Quinn signed a new state law intended to crack down on individuals who use social media to organize so-called "flash mob" violence. Earlier this spring, two dozen teens were arrested in the same area of downtown Chicago for randomly attacking both each other and pedestrians.
According to DNAinfo Chicago, penalties for such "mob" organizers will increase from one to three years in jail to three to six years under the new law.