Police responded to reports of disturbances near Michigan and Chicago Avenues.
Police said 28 teens were arrested during the incident and no serious injuries were reported.
The teens charged with misdemeanor reckless conduct and battery and later released, according to News Affairs Officer Perkus.
Eleven other teens were charged with the same misdemeanor charges after they attacked a group of women on the CTA Red Line, police said.
"You have over three to four hundred teenagers with mob action, jumping on individuals that are downtown," said community activist Andrew Holmes. "Multiple people have been arrested and I caution those parents that get this call about your child being arrested -- maybe you need to check your child."
Officers began breaking up the attacks by ushering teens to the Red Line. Chaos continued underground but many attackers reportedly left the area.
"I just saw a cluster run down to the Red Line," said Red Line passenger Amanda Dobson. "I didn't know what was going on. I just kind of stepped back and let the police do what they needed to do."
Police continued to patrol the area on bikes, horses and on foot as smaller groups wandered around the Loop.
It is not clear if the attacks are related to a similar mobbing of Ford City Mall last month.
Residents were concerned that this could be the first in a long line of attacks after warm weather brought on a string of similar instances last year.
"It's been happening a lot around here," said Eric Baldinger, who works along the Magnificent Mile. "Just keep your wallet close and your purse closer."
Others said the attacks were disappointing and feared for the future of the city.
"I think it's very childish," said resident Angelica Wilson. "That's what wrong with the generation today because there's always petty fights going on down here and everybody getting hurt. We don't need more problems."