Police have visited five properties in the city suspected of housing ‘pop-up brothels’.
It comes as a national week of action is launched to target those being sexually exploited in the city.
Lancashire Police say the rise of the brothels, which move from rented properties to hotel rooms, is linked to adult websites and the use of social media and messaging services.
During Monday (24 September) police visited addressed in Deepdale, Ribbleton, Moor Park and Avenham. No arrests have been made at this stage.
The use of the brothels are often linked to human trafficking and the exploitation of migrant women brought to the UK to work as sex workers.
In March 2016 three men were convicted and jailed for a total of 53 years for forcing two young Romanian girls to work as prostitutes.
A property in Longworth Street, Deepdale, was rented out and Marius Petre, Adrian Matei and Ionut Ion repeatedly raped two 18-year-old girls and forced them into sex work.
In December last year three Preston men were jailed for their role in a human trafficking gang.
A website was used to run a ‘pop-up brothel’ in Blackburn, and also advertising the women, all from Romania, for visits to hotels and other addresses across Blackburn and Preston.
Florinel Mitru, Traian Gavrila and Marius Dide were all jailed for their role in human trafficking and sexual exploitation of women.
Read more: Preston pimp who ran brothel on quiet Fulwood street is jailed
In June this year a Preston man was jailed for his role in a seven-strong human trafficking gang who moved prostitutes around the UK to work in brothels.
Detective Sergeant Abi Finch-Hall of the Lancashire Police human trafficking and modern slavery team said: “Some adult sex websites are used by sex workers to advertise their services online. The highest proportion of advertisements relates to women.
“Often rented properties or hotel rooms are used on a short term basis as a place to sell sex, hence the term ‘pop-up brothel’. Some people who advertise in this way may be victims of sexual exploitation, a form of modern slavery, in which they are controlled by their exploiter and forced to in to prostitution with no freedom of choice.
“We want to ensure the safety and wellbeing of potential victims and will be targeting addresses throughout Lancashire to achieve this.”
“We want to offer help and advice for people who think they may be victims of human trafficking or slavery.
“You may be a victim if someone is controlling where you live or your money or with-holding your travel or identity documents from you. If they are controlling where you go, who you speak to, what you eat, you may be a victim.
“If you are frightened or are being threatened by others who are making you work there are people that can help you.
“As a victim you have rights and help and advice is out there. Help can be in the form of safe temporary accommodation, medical treatment or a translator to help you to communicate. You can also be provided with some legal advice.
“There are a number of ways you can contact someone for help. You don’t have to speak directly to the police there are charities that can help you. You can also ring some services anonymously; you do not have to give your name or go to court or give a statement.”
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Clive Grunshaw said: “Tackling modern slavery and human trafficking is a key priority for us in Lancashire, and this week of action is another sign of the work being done to help those being exploited and bring offenders to justice.
“I am proud that the resources I have put into this fight places us at the forefront of anti-trafficking work, making our communities safer, with the action taking place this week also highlighting the need for agencies and organisations across the county to work in partnership.
“By working together, sharing information with the authorities and supporting victims we can tackle this serious and often hidden crime.”
Read more: How to tell if you’re living near a ‘pop-up brothel’
Anyone needing advice, support or who has suspicions about a premises or something in their community should call the modern slavery helpline on 08000121700. You can also call the police on 101, or if you believe someone is in imminent danger call 999.