At least a dozen cases of the growing phenomenon have been recorded across the county this year, according to local police, who believe the figure is just the tip of the iceberg.
They are backing a national campaign to encourage more victims to come forward by assuring them they are not alone and need not fear judgement.
Paul Leonard, major incident room office manager at South Yorkshire Police, said criminal gangs overseas were assuming fake web personas as attractive young women to lure unsuspecting victims – typically men aged 17 to 25, and sometimes as young as 14.
He said the predators would often stalk their marks by researching them online to appear more convincing, before striking up a relationship over the internet and seducing them to get them to perform sex acts.
They are then recorded without their knowledge and threatened that if they do not hand over money the footage will be shared with friends and family. Police say they know of at least four suicides in the UK linked to this form of web blackmail.
“We recognise the victims may be feeling vulnerable and experiencing shame and anxiety but we’re here to help you. You’re not alone and you won’t be judged,” said Mr Leonard.
“It’s tragic to think there have been suicides where young men who have been victims of this sinister crime felt they had nowhere to turn.
“We don’t want anyone to feel like that. Come to us and we will do everything in our power to find out who’s behind it.
“There are 12 cases which are under investigation after being reported this year in South Yorkshire, but I’m convinced there are many more victims out there who have decided not to report it and I would urge them to come forward.”
Recorded cases of financially motivated webcam blackmail have more than doubled in the UK over the last year, with 864 so far in 2016, compared with 385 during the whole of 2015.
But the National Crime Agency and National Police Chiefs Council believe thousands of people are likely to be falling prey each year, with many failing to report the matter.
They have launched a national campaign encouraging more blackmail victims to come forward and warning those at risk to be careful about who they befriend online and especially who they share intimate details with.