"CPD arrested 1st of several juvenile offenders in Facebook sexual assault incident," police department spokesman Anthony Gugliemi wrote on Twitter late Saturday.
The boy, who is 14, faces at least three juvenile felony charges, The Chicago Tribune newspaper reported, citing city police.
The victim was a 15-year-old girl who went missing on March 19 in the crime-plagued midwestern US city. She was found two days later and taken to a children's hospital for treatment.
Gugliemi promised more details at an 11 am (1600 GMT) Sunday press conference.
City police got involved when the girl's mother approached police with graphic photos taken from a Facebook Live video showing several young men assaulting the teen.
It was the latest in a series of troubling incidents in which violent acts have been streamed live on Facebook, including two fatal shootings and the kidnapping and torture of a disabled 18-year-old.
The live online video of the alleged gang rape attracted as many as 40 viewers at one time, but no one contacted police, according to reports. The video was later taken down.
Chicago has been grappling with a surge in violent crime. Last year, the city endured its highest number of shootings and murders in nearly two decades.
Much of the violence is concentrated in a few impoverished areas, including the one where the teenage girl lives.
(This story has not been edited by NDTV staff and is auto-generated from a syndicated feed.)