The attack took place in a South Side alley and was posted online. The teens allegedly beat and robbed a 17-year-old.
Six of the juveniles were charged last week. A seventh was charged Monday.
According to the Cook County state's attorney, the latest person charged is the brother of one of the other suspects.
An attorney for one of the suspects spoke after Tuesday's hearing.
"They're remorseful. It's something that got out of control, got out of hand. I think that when you're a child and you're impulsive, I think a lot of these type of occurrences take place," said Peter Garbis.
The victim suffered non-life threatening injuries.
Seventeen-year-old Raymond Palomino is charged as an adult in this case.