Popular virtual game Roblox is a hunting ground for sex offenders looking to exploit young New Zealand-based victims, according to an online safety group.

Roblox users can create an avatar or online character and choose their hair, clothes and accessories, before joining in a number of games or experiences.

The platform also had a social media element to it where people could message, accept friend requests, or go into a chat room.

Police would not name specific gaming sites, but Detective Senior Sergeant Kepal Richards from the online child exploitation unit said there had been cases of sex offenders grooming young New Zealand gamers online, encouraging x-rated conversations and the sharing of inappropriate images.

"The offenders, for example, will use these gaming platforms or social media applications to strike up conversations in relationships with young people before requesting to move their conversation to another application or messaging service," he said.

"Once here, they'll engage in indecent communications; they'll share or encourage the sharing of [sexually] explicit imagery [and] other criminal offences, such as blackmail in the form of sextortion."

New Zealand children did often fall victim to this kind of offending, he said.

"We get referrals out of the National Center for Missing and Exploited Children, which is based in America, and they routinely see instances where children have been targeted on such sites as gaming applications or also social media websites."

Predators could groom children to go into a private chat room, he said.

"Some of the gaming applications, for example, don't allow the sharing of imagery, so these offenders will encourage them to go to applications or messaging services that do allow that to happen, such as video calling or the sharing of photos.

"It's there that they'll start to encourage the sending of sexually explicit material, or just taking the conversation to an indecent nature."

Our Kids Online co-founder Rob Cope told Checkpoint Roblox was one of the biggest sexual predator grooming grounds in the world.

After giving hundreds of talks across the country, parents, school teachers and principals had approached him with stories.

"A lot of them, if they're not to do with social media, which is like a massive problem, then it's Roblox.

"One principal, in particular, said there were three Year 8 girls who all sent nudes to the same predator on Roblox over a very short period of time."

The girls were aged between 12 and 13 years old.

"I think the avatar's name was something like Handsome Stranger or something - it was pretty obvious to an adult that's probably not a great person to be talking to online," he said.

"The thing with Roblox is they fully deny that any of this actually happens, which is weird because any online platform where you can talk to strangers there's going to be predators on there, hunting."

Roblox is a popular game among children. Photo: RICCARDO MILANI / AFP

When he was making a documentary a few years ago, Cope said many people told him about "sex rooms" that could be found on Roblox.

"I just went on to YouTube and typed in Roblox sex and there are a whole lot of different videos where people who had been in these and they just video captured what was going on."

It was an aggressive form of grooming, he said.

"I mean, predators would describe it like it's shooting fish in a barrel because most of us parents would just let our kids on Roblox and think it's a harmless game.

"The whole concept of Roblox is it's a fun game. It's a social game. You're walking around talking to strangers all the time, but a predator is going to hunt where their prey hang out, right?"

To combat this, parents could lock certain controls down, so children communicated only with their friends, he said - however children's friends may also be strangers.

"A lot of kids will just make friends with complete strangers online, because someone will friend-request them. They go, 'Cool, we've got another friend.'

"The parents might be locking down, 'OK, you can only talk to your friends.' But your kid has 500 friends on Roblox.

"I remember my son, when he was about nine, he's playing Roblox, and one day he goes, 'Dad, I've got 100 friends on Roblox.'

"I'm like, 'Wow, that's a lot - and how many of these people do you actually know?' He [said], 'Three.'

"I'm like, 'Right. So you're friends with 97 strangers?' "

In Roblox, users could speak to other avatars in the virtual world.

"There's ... speech bubbles above everyone and as you walk past, you can just stand right next to someone and type in something in the computer and it will come up as a speech bubble above your character," he said.

"You can even actually talk to people on the game as well, like voice to voice. All you have to do is have a phone and say that you're 13 years old and they'll send a code to your phone, and now you're verified as a 13-year-old and you can voice talk to people, so you can literally be physically talking to strangers online as well, not just messaging."

There were supposedly different age levels in the game, but anyone could access them, he said.

"There's nine-plus, 13-plus, 17 plus, but I think anyone can get into it. I'm not that familiar with it. I just hear the horror stories from parents and principals."

Parents were unable to tell how old an avatar was and where they were, he said.

"I always tell parents, the main thing you need to do is no devices in bedrooms or bathrooms at all. If your kids [are] playing any kind of game, that should be out on the kitchen table where you can see what's going on, it's being monitored. You're looking over their shoulder every once in a while; you have the rules.

"A predator will sneak in with a kid and become their friend, and then you'll become that friend. Because you'll say, oh, no, I know this person. It's a friend of a friend, but you don't actually know that person.

"I kind of say to parents gaming's cool, it's fun. But it's like ice cream. It should be something you do every once in a while and you have a little bit. It's not something that you're doing for hours and hours a day."