Image copyright ABC

A second teenager is in custody in Chicago for an alleged sexual assault that was streamed live on Facebook.

The 15-year-old suspect's mother drove him to the police station on Monday afternoon, a police spokesman said.

A 14-year-old boy has already been arrested over the alleged assault, in which a girl was attacked by up to six males with 40 people viewing it online.

Each faces charges of criminal sexual assault and the manufacturing and disseminating of child pornography.

Neither of the suspects nor the victim has been named due to their ages.

She and her family have had to move home after facing a barrage of online and in-person harassment, police say, and the alleged victim has been unable to return to school.

"The young men responsible should be ashamed of themselves," said police chief Eddie Johnson.

"They've humiliated themselves, humiliated their families, and now they're going to be held accountable for what they did."

In January, Chicago police arrested four people following a separate incident in which a man's alleged assault was live streamed, also on Facebook Live.