One in five people aged between 10 and 17 have experienced signs of online grooming, and one in 10 within the last year, Claire Lister from the eSafety Commissioner said, detailing the preliminary findings of a major study.
Adults doing or saying something creepy was the most prominent approach but children were also asked about private parts of their bodies and for nude images, including for money.
The child didn't know the person in real life 70 per cent of the time, although some characterised strangers as "an online friend".
Half of perpetrators started by talking about other things and almost 60 per cent were found to use deception, including convincing the minor they were younger than they were or had similar interests.
Only half of children told someone about their experience and only a quarter reported it.
Some were scared they'd be punished and banned from using the platform or their devices while one in five said they were embarrassed or felt shame.
Parents needed to avoid a punishment response that's acting as a barrier, Ms Lister told the reducing online harms conference hosted by the Australian Institute of Criminology in Canberra on Tuesday.
When it came to sexual harassment online, nearly one in three young people said they had been a victim and one in five had experienced it in the last 12 months.
This included receiving sexual messages or being asked to send nude images.
Teenagers are also at risk on adult dating apps - where users are required to be 18 - with children as young as 12 skirting age requirements, the conference heard.
Minors had lied about their age and signed up to flirt, find sexual encounters, make money on "sugar baby" sites and for excitement or out of boredom, Dr Tahlia Hart from Flinders University said.
"Adult-based platforms are affording these opportunities but they don't necessarily appear to be the instigator of them," she said, adding it was still a risky environment where they were susceptible to being groomed.
Dr Hart queried why dating apps weren't captured by the government's social media age ban, which forces tech platforms to verify the age of users to block people under 16.
She called for companies and app stores to take more steps to stop underage users accessing platforms and for the government to look at mandatory age limits.
More broadly, three in four people had experienced dating app-facilitated sexual violence, the Australia Institute of Criminology's Heather Wolbers said.
The term encompasses sexual harassment, abusive language, image-based sexual abuse, stalking and rape.
LGBTQI people reported the highest rates of sexual violence in this context, she said.
Dating apps brought a lot of people together so perpetrators could suss out vulnerable users and there was a lack of guardrails or reporting mechanisms to prevent this, the researcher said.
"Offending can be quite concealable," Dr Wolbers said.
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