BOGOTA (REUTERS) - Instead of lurking in shopping malls and parks, predators who befriend and sell children for sex now hang out on social networks such as Facebook and gaming sites, said experts fighting to stay one step ahead of rapidly-evolving criminal gangs.
Colombian traffickers used to pose as rich, older men promising a better life; now they pretend to be poor, troubled teenagers just like the children they target, said Mr Sebastian Arevalo, head of anti-trafficking group Pasos Libres Foundation.
"Trust is now gained through empathy and emotions," the Bogota-based Mr Arevalo, who has talked to hundreds of students about the dangers they face online, told the Thomson Reuters Foundation.
"Recruiters are of similar age (to their victims). They say,'I too have problems at school and with my parents', 'I've also broken up with my partner'."
From the United States to the Philippines, a soaring number of young people are being trafficked online, fuelled by the global spread of cheap, high-speed internet and rising mobile phone ownership, particularly in developing countries.
About 750,000 sexual predators worldwide are online at any given moment, the US-based International Centre for Missing and Exploited Children said last year, often grooming children for sexual abuse as a first step to enslaving them.
Grooming involves befriending children, mostly aged 11 to 15, to gain their trust, before luring or coercing them to send sexual images or videos of themselves, which are shared online on password-only group networks and websites, experts said.
"Grooming is the precursor phase," said Mr Hernan Navarro, head of campaign group Grooming Argentina, which educates parents and children about the risks of social media.
"It's the gateway to more serious crimes like human trafficking," he said.
After starting a seemingly innocuous online friendship, children sometimes go on to meet their virtual "friend" in hotels, cafes or parks, which can lead them to being trafficked and sold online, according to campaigners.
A third of all Internet users in the world are aged under 18, according to the International Centre for Missing and Exploited Children, which has trained more than 10,000 law enforcement officers and specialists to investigate child sexual abuse.
"The seducing process often starts online," said Mr Fabio Gonzalez, Latin America coordinator at the anti-child trafficking group ECPAT International.
"Traffickers are recruiting children where they interact with their peers, which is a virtual environment."
Children who have suffered prior abuse, and who come from poor backgrounds and broken homes are most at risk of falling prey to traffickers on the prowl online, experts say.
Last year, one in seven children reported missing in the United States was likely a victim of sex trafficking and most were in the welfare system when they disappeared, according to the National Centre for Missing and Exploited Children (NCMEC).
"Facebook is really a primary social media medium for traffickers to engage susceptible and vulnerable victims into the trade," said Mr Kevin Campbell, vice-president of global operations at anti-trafficking group The Exodus Road.
Mr Campbell's colleague, Julie, spends hours a day trawling through websites advertising sex and massage services, using cyber forensic tools such as facial recognition software and data scraping, to gather information about trafficking gangs.
Sometimes the words "young", "sweet", "college" and "new" are red flags, other times it is the same telephone number or photograph being used in adverts in different US cities.
"We try and trace people through certain areas - is this person being moved from one city to another?" said Julie, who declined to give her real name for security reasons.
"We look for those clues to help us piece it together. We really want to find the traffickers that are handling not just one victim but many victims."
Numerous groups and telecommunication companies are working to educate parents and children on safe ways to use the Internet and mobile phones, including the use of parental controls to monitor activity and block sites.
Internet companies can block access to domains containing child sexual abuse material using a list compiled by Interpol.
But seven out of 10 people in Argentina do not even know what grooming is, according to Grooming Argentina, even though the Latin American country passed an anti-grooming law in 2013 that carries four-year prison sentences for offenders.
And two-thirds of the world's countries have no specific laws to combat online grooming of children for sex exploitation, while globally there are few convictions for the crime, said the International Centre for Missing and Exploited Children.
"Children don't recognise themselves as victims," said Grooming Argentina's Mr Navarro, adding that parents have a key role to play in educating their children about the dangers.
Spanish telecommunications giant Telefonica hosts workshops in schools in Latin America and Europe teaching children about the risks of encrypted instant messaging services like WhatsApp that allow users to remain anonymous.
The online gaming industry has also taken steps to help prevent grooming, including safe chat functions and in-game chat moderators who monitor online conversations.
Poptropica, a multi-player online game for children, only allows users to send scripted messages rather than chat freely.
Despite increased efforts to raise awareness among children, parents and teachers about using the Internet safely, campaigners face an uphill battle to tackle online trafficking.
Websites that are closed, such as the sex ads marketplace website Backpage.com which was shut down in April by US authorities, are likely to be replaced by others, experts say.
"We're just waiting for the next one to pop up," said Julie the cyber analyst. "It's only a matter of time. Traffickers have something to sell, they just have to find a place where they can sell it."