Story highlights Police: Teen knew at least one -- and possibly more -- of her alleged attackers

Girl has been reunited with her mother after receiving treatment at a hospital

(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.

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