A 17-year-old Soweto girl with the mental age of a four-year-old who was gang-raped on film has been found captive in another man's home, police said.

"She was found with another man in his house in Braamfischerville," the CapeTimes quoted Warrant Officer Kay Makhubele saying.

Makhubele said it appeared that the girl had been kept against her will by the man.

"Obviously she is traumatised and we are going to take her to the doctor," Makhubele added.

The man was charged with abduction. Police will determine whether a rape charge would be added.

This brings to eight the number of arrests made since the graphic video showing the girl being gang-raped was posted online.

Seven people aged between 14 and 20 were arrested in Dobsonville on Tuesday based on video identification.

The girl disappeared from her house three weeks earlier.

South Africa's Women, Children and People with Disabilities minister Lulu Xingwana condemned the attack.

"This despicable crime does not belong to our free and democratic society. In addition to the painful ordeal of rape she was forced to endure, she is now subjected to a second assault on her dignity.

"We must all spare a thought for this young girl who has been violated in such a cruel and inhuman way."

Faith Mazibuko , a member of the Gautang legislature who examined the girl, said the victim had the mental capacity of a four-year-old, Eye Witness website reported.

Mazibuko said the girl was calm but hungry, according to the report.

"She says she was kept as a sex-slave," Mazibuko added.