WARNING: This story contains explicit references

A 3 News investigation has uncovered a group of young Auckland men publicly recruiting other boys to join them in group sex sessions with girls - some of them underage.

They're using Facebook to not only recruit, but to name names and publicly humiliate their female conquests.

The 17 and 18-year-olds call themselves the "Roast Busters", are unashamedly proud of their exploits, and not afraid to tell all.

"We take what we do seriously, some of you think this is a joke, it's not," says one of the young men in a video uploaded to the social networking site.

"You try and get with the amount of girls we do. This is hard, it's a job, we don't do this shit for pleasure."

The group was formed in 2011, and police admit to 3 News they've been investigating them ever since.

Five months ago the Roast Busters started using Facebook videos to name the often-drunk underage girls they claim to engage with.

And they're calling for more boys to join them.

"A true roast is where you know you are going there intentionally to roast this female," says one young man in a video. "We don't choose a roast, the roast chooses us. We have girls hitting us up to 'hang out with us'. They know what we're like; they know what they're in for."

One young girl will tell you otherwise.

To protect her identity we can't tell you when or where she encountered the Roast Busters; just that she was underage - and police say she's one of many potential victims they're aware of.

"I just kept blacking out 'cause i had drunken too much," she says. "You could say I got raped. I had sex with three guys at one time."

Police admit they have interviewed a number of girls over a two and a half year period about the Roast Busters. And they've been monitoring the group's Facebook page, which they describe as morally objectionable but not criminal.

When 3 News contacted Facebook on Thursday, it was shut down two hours later.

"None of the girls have been brave enough to make formal statements to us so we can take that to a prosecution stage," says detective inspector Bruce Scott. "Clearly they are traumatised by what's happened.

"We would love to take some positive action for these girls and others who may be victims in the future, but without actual evidence my hands are tied."

For cases to stand up in court police maintain they need formal statements. In the meantime, they have issued a warning to members of the group.

"We've told them their behaviour is verging on criminal if not criminal, and suggested it cease," says Mr Scott. "Some of the boys and their families were compliant and we believe they have stopped associating with the group."

Other young men have not taken the warning on-board.

"My first actual roast for the Roast Busters was bad, it was fun, I felt like the man," says one of them. "I thought this is going to go big, everyone is going to know about the Roast Busters."

And maybe they will -- but for all the wrong reasons.