Posing as a paedophile, Tony Kirwan trawls brothels in search of underage girls.

Raised in a devoutly Christian family, Tony Kirwan had a sheltered upbringing.

Not once did he see his parents walk into a pub or even let alcohol pass through their lips. It was, in his words, “a wrapped-in-cotton-wool sort of life”.

The past 16 years, though, couldn’t be more different for the former electrician.

The Queensland man has devoted his time to trawling dark, seedy brothels in south east Asia on a mission to liberate and rehabilitate as many underage sex trafficking victims as he and his organisation, Destiny Rescue, can manage.

UNICEF estimates that there are approximately 1.2 million children lured into the sex trade each year, and up to 100,000 of those are in the Philippines alone.

It’s there that SBS current affairs program, Dateline, embedded with Kirwan as he gathered evidence of child exploitation to deliver to under-resourced local police. Joining Kirwan, journalist Amos Roberts posed as a paedophile in an effort to root out victims and abusers.

"I don't think I anticipated quite how icky and how grim it would feel going out with those guys, given what they were trying to do - to find under-age girls who were doing sex work," Roberts told Mamamia. "When you're in a brothel or you're in a bar and they're asking you if you fancy anyone, if they can bring you a girl... I'm like, 'Oh no, I'm sorry. Not right now. I'm a bit shy.'"

Though Kirwan and his colleagues perform this baiting charade regularly, for Roberts the level of discomfort at even pretending to live in that skin was intense.

"I mean, people are out there thinking that you are what you're not," he said. "People are making assumptions about you, thinking that you're a paedophile. It is just a horrible thing. Horrible for them as well to be confronted with it."

In the course of filming in Manila, a Swiss backpacker began talking to him and Kirwan on the sidewalk outside a local karaoke bar - a bar fronted by a group of women offering massages. He was looking for conversation, for company with whom he could share a drink inside. But dedicated to his role, to his mission, Kirwan replied, "We’re looking for girls a bit younger than this. Gettin' fussy in me old age.”

"[The backpacker] just vanished. I've never seen anyone run away so fast," Roberts said. "On the one hand, given that he was just sort of a normal backpacker it seemed a bit gratuitous to say that to him, but that is how they end up in conversations with [paedophiles] who feel comfortable telling them what they do.

"Because once once they feel safe with you they sort of open up to you about the things that they've done and the things that they want to do. Tony said it takes pretty much all of his self-control not to blow up and do something violent."

Ultimately, embedding themselves this way is the most effective tool Kirwan and his colleagues believe they have in their effort to liberate underage girls. It took Kirwan six months of trying to realise that he couldn't just walk into brothels and lead them out.

"They just didn't trust him. So there's a very long process when it comes to those kind of rescues - soft rescues they call them - of winning over the trust of the girl," Roberts said. "He's told me about times that he's sort of driven away with [a girl] and they've told him later that they spent the entire drive sort of clutching a little pocket knife or something just in case he turned out not to be who he said he was."

So far Destiny Rescue claims to have liberated nearly 2000 children enslaved around the world. It's a small, but meaningful dent in an incredibly broad and complex problem.

"When you look at what can be achieved in terms of the resources, the time and the effort that goes into sort of just rescuing handfuls of children, it is pretty difficult," Roberts said. "But I guess that's one of the special qualities that people have to work in this area.

"Tony and his organisation Destiny Rescue talk about wanting to end child slavery. There's a level of faith and optimism that motivates them. And I guess it's a belief that people here can see stories like this and can realize that there are people that are trying to do something about it and they can support those organisations, then the more support they receive the more the more help they can give."

Dateline, 'How to catch a pimp', airs Tuesday 12 June at 9.30pm on SBS. The program is available after broadcast anytime, on your favourite device via SBS On Demand.