West Midlands police say eight men have come forward saying they were lured into video chats and then blackmailed

Police have warned men to be wary of online "sextortionists" who blackmail victims by threatening to post explicit footage of them on the internet.

Eight victims have contacted West Midlands police in recent months after being instructed to pay thousands of pounds into offshore bank accounts. Officers say the blackmailers lured men into online video sex chats and then sent screengrabs to them along with demands for cash.

One man faced a demand for $5,000 (£3,000) from offenders who threatened to email images to his girlfriend and his daughter.

The offenders usually target their victims on social media sites such as Facebook and through conversations on Skype or FaceTime.

Detective constable Stefan Ashton, of West Midlands police, said: "Since January we've seen a rise in the number of these offences in the West Midlands, with victims in Wolverhampton, Birmingham, Dudley, Walsall and Coventry.

"In most of the cases, the videos have not actually been distributed, but it's nevertheless been an absolutely horrendous ordeal for the people involved, who are understandably very worried about the consequences of such images and videos being posted online.

"The damage in the cases where the footage was shared with the victims' Facebook friends cannot be underestimated – they are clearly devastated. The blackmailers are calculated and malicious and have complete disregard for the people they're exploiting."

He added: "Cases of this type are notoriously complex, and because IP addresses are usually traced back to foreign countries, they often, despite our best efforts, go unsolved.

"We are working closely with partners such as the National Crime Agency to crack down on offenders but the only real way to prevent this from happening is by not taking part in such activity at all. The moment you reveal yourself in an online video, you become vulnerable to exploitation and sadly it's the blackmailers who instantly become in control of the situation."