By Emanuella Grinberg and Samira Said

CNN

(CNN) -- Chicago Police are searching for as many as six people involved in the sexual assault of a teenage girl that was broadcast on Facebook Live, a police spokesman said.

The video shows at least five to six males -- some possibly juveniles -- sexually assaulting the 15-year-old, police spokesman Anthony Guglielmi said.

At least 40 people were watching the live stream at one point and no one called police, Guglielmi said.

The video came to light after the girl's mother approached Chicago Police Superintendent Eddie Johnson on Monday as he was leaving 10th district headquarters. She told him her daughter had been missing for 24 hours, Guglielmi said.

She showed Johnson screengrabs of the live broadcast, which indicated that at least 40 people were watching at the time. The images distressed Johnson, a father of two daughters, and he brought the woman inside to file a report.

Victim and mother reunited

Since then, the teen has been reunited with her mother. She is being treated in a hospital.

Some people are identifiable from the video, Guglielmi said. The teen knew at least one of her alleged attackers and may have been acquainted with the others.

Police contacted Facebook, Guglielmi said. The video is no longer on Facebook.

A Facebook spokesman said, "Crimes like this are hideous and we do not allow that kind of content on Facebook. We take our responsibility to keep people safe on Facebook very seriously and will remove videos that depict sexual assault and are shared to glorify violence."

It's not the first time an incident has come to the attention of Chicago Police via Facebook Live. Four people were charged in January in an attack on a special needs teen that was streamed on Facebook Live.

According to its community standards, Facebook removes content, disables accounts and works with law enforcement in cases of genuine risk of physical harm or direct threats to public safety. Facebook users also can report offensive material to staff dedicated to responding to such reports. If a live stream starts blowing up, staffers monitor it for possible violations and interrupt it if need be.