Crimestoppers has issued an appeal for information on pop-up brothels operating across South Yorkshire.
The charity wants information to pass on to South Yorkshire Police and neighbouring forces across Yorkshire and Humberside in a bid to stop women from being forced to work as sex slaves against their will.
Crimestoppers said the brothels tend to be run for a short time from newly-acquired properties, often privately rented flats or houses.
Budget hotels or holiday properties are also sometimes used, according to the charity.
It claims that many of the women forced to work in the brothels are Eastern European, Thai and Nigerian.
Gemma Wilson, regional manager for Crimestoppers, said: “These brothels are dens for criminals to recruit and house vulnerable women who are then put through ordeals no woman should have to go through.
“People who run these brothels run them within our communities, think they can get away with it, and have no limits as to what they will do to their victims.
“On the victim’s behalf and that of Crimestoppers, I’m appealing to people who might have information on those running these brothels, so we can shut them down and give the victims some hope of getting their lives back.”
She said there are a number of signs which could indicate that a pop-up brothel is operating.
"There are a number of signs which could indicate a pop-up brothel is being run - limited activities usually associated with new people moving into a property, for example no removals and properties which are limited or scarcely furnished, appearing as though no one actually living there.
"Multiple women living at the address, or who may be brought to and taken from the address by an individual; multiple vehicles visiting the property at any one time and many frequent visitors, usually male, who don’t stay for long periods of time."
Anyone with information should call Crimestoppers on 0800 555 111.