Police have admitted they received a formal complaint from a victim of the Roast Busters group two years ago, but are adamant they did not have enough evidence to lay charges.
Since 2011, police have been monitoring the Auckland group of 17- and 18-year-old men who have boasted online about sex with intoxicated girls, some of them underage.
Until now, police have said they haven't received any formal complaints about the group and have appealed for victims to come forward.
But a 15-year-old girl told television's 3 News on Wednesday night that she complained to police two years ago of a sexual assault by members of the group when she was 13.
"They said that I did not have enough evidence to show because I went out in clothes that were pretty much asking for it. I was asked a lot of questions about what I was wearing (including) why did you go out in a skirt."
The girl said if her complaint had led to charges, it would have prevented other girls from being assaulted.
"I can't believe that nothing was done then - because from then on, I've had my friends being sexually abused by them. I've heard of how many girls being raped, sexually abused.
"I've seen posts by my friends saying that the Roast Busters ruined their lives. And if something had been done when I'd gone in, that would have never happened."
Police have confirmed that they received the complaint, but said there wasn't enough evidence to prosecute.
They said the allegation of inappropriate and offensive comments made to the girl is being investigated.
Commissioner seeks assurance
The Chief Human Rights Commissioner has asked for an assurance that police have properly investigated the group of young men.
David Rutherford told Radio New Zealand's Nine to Noon programme he has questioned Police Commissioner Peter Marshall about the investigation.
Mr Rutherford said he wanted to assure himself that the appropriate evidence-gathering steps were under way.
"But also, more importantly actually, that he was satisfied that the victim support that was necessary was wrapped around these young people."
Mr Rutherford says he was satisfied with the answers the police commissioner gave him.