Gangs are using social media sites such as Facebook to lure young women into crime and prostitution, the head of European policing agency Europol said on Wednesday.
Rob Wainwright said traffickers were drawing victims in by posting advertisements for childcare or cleaning vacancies and once ensnared, controlling their movements with webchats and webcams.
"They are using modern technological tools to more efficiently monitor an increasing number of victims," Wainwright told the Centre for Social Justice think-tank in London.
"So instead of paying them a visit every day they can use webchat services and also webcams to confirm that they are where they should be, in that brothel waiting for the next customer.
"In the past pimps and traffickers had to do that by physically visiting them. Now they can just do it at the click of a button and therefore control 50 victims much more easily and readily in virtual form," he said.
The police chief said criminal gangs regarded trafficking as a "low-risk, high profit" venture, which generates around $150 billion a year for criminal gangs.
Most of Europe's estimated 500,000 victims are from Romania, Bulgaria and Hungary with Britain, Germany, Belgium and the Netherlands the most likely destinations.
Wainwright called for an international effort to tackle the problem.
"As things currently stand, organised crime groups are going about the business of modern slavery with little fear of being caught and pursued. We urgently need to do much better," he said.
"There is no point in sitting on a vital piece of information in one country if it can break a syndicate spread across five or more others. The culture of policing must change," he added.