The posters, featuring an image of a brothel and the strapline "Walk in a punter. Walk out a rapist" were piloted yesterday in men's toilets in pubs and clubs in Westminster and Nottingham.
The ads, created by Rainey Kelly Campbell Roalfe/Y&R, urge men to call Crimestoppers if they suspect a woman has been trafficked with the line: "If you're man enough, call Crimestoppers."
The poster campaign will be supported by online ads and also points people towards the UK Human Trafficking Centre's for more advice.
The Home Office said that a key part of the UK Action Plan on Tackling Human Trafficking is to undertake publicity and awareness-raising to reduce demand in the UK.
The evaluation of the pilot marketing campaign will feed into a six-month review which began in January looking at what more the Government can do to tackle the demand for prostitution.
Vernon Coaker, Home Office minister, said: "Trafficking is a vile and evil trade and sex buyers must be made to think twice about the consequences of their actions.
"The advertising campaign should help draw attention to the plight these women face and make men think again about what they are doing."