A group of adults extorted a network of 140 teenagers, some as young as 13, for sexual acts, West Australian police allege.
Investigators from the force's Sex Offender Management Squad began inquiries in April to find out whether 'Reportable Offenders' - convicted sex offenders who have to report their movements to police - were meeting their obligations.
They discovered a group of 11, including four who were already registered child sex offenders, had made contact via Facebook and Instagram with 140 teenagers aged between 13 and 19.
Police alleged one of the offenders physically met with a victim.
Of the 140 youths, 23 are alleged to have been the victims of sexual offending.
WA police have laid more than 200 charges on the group, who are aged between 18 and 41. About a third of the alleged offences are sexual in nature.
They say the probe has highlighted the importance of cyber safety and for parents to be aware of who their children are talking to online.
"Mobile phones and the ongoing rise of social media platforms provides offenders with new ways to reach out to youths in order to commit crimes and we're working hard to crackdown on this behaviour," Acting Detective Senior Sergeant Matt Daly said on Saturday.
A WA Police video shows police busting into offenders' homes and arresting them.
Those who are already convicted sex offenders are subject to mandatory reporting with strict limits on contact with children. Breaching these obligations can lead to imprisonment.