Organisations campaigning against child sex trafficking are appealing to police and social workers across the UK to be more vigilant.
Many children are at the mercy of criminal trafficking gangs
There is evidence that criminal gangs from Africa have begun targeting cities beyond London and the South East.
The gangs who traffic children as sex slaves are even using voodoo to frighten them into prostitution.
The international charity Unicef believes the problem is growing and is calling on the government to bring in new laws to protect the victims of child trafficking.
The BBC's social affairs correspondent Kim Catcheside told Radio 4's Today programme that spells are being cast over the teenagers to scare them.
"The traffickers have to terrify the children into submission, and the use of rape and physical violence, the threat that the family back home will be hurt if they don't obey, is all used.
"This is compounded by essentially putting voodoo spells on them, taking bits of hair and nails and wrapping them up in a parcel, the belief being that whoever holds this parcel has power over you."
Gangs were becoming wise to police tactics to stop the sex trade, and were moving away from London to centres like Newcastle and Nottingham, where they would stay until it was safe to move the children out of the country, she said.
In Nottingham, an inquiry is underway after five teenage Africans were found abandoned by a suspected human trafficking gang.
The four girls and a boy, aged between 14 and 18, were found over a period of six months.
Detectives believe that one of the children had already worked as a vice girl in the South East and said the group may have been left in Nottingham with the intention of moving them on at a later date.
Currently, trafficking children is not a crime under UK law, which is outrageous
In Newcastle, the authorities have seen 25 children in the past few months, eight of whom have led police to believe that they have been brought to the UK for sexual purposes.
Ms Catcheside said a full-time child protection officer was now in place at Heathrow airport, working with immigration officers to identify suspected child traffickers and their victims.
"You need someone who knows the signs to look out for and to intervene," she said.
Thousands of children are believed to be trafficked to the UK every year, mainly from West Africa, Eastern Europe and Asia.
Children and their families are usually unaware of the real fate the victims are awaiting, and promises about education and a better future are rarely kept.
Under its End Child Exploitation campaign, Unicef UK is asking for safe houses, counselling and education to be provided across the country.
Spokeswoman for Unicef Soraya Bermejo, said: "Currently, trafficking children is not a crime under UK law, which is outrageous.
"It is less dangerous for the criminal to traffic children than drugs, because trafficking children is not an offence, unless it can be proved that there have been sex offences.
"A new sexual offences bills is currently going through the House of Commons, where hopefully things will be tightened up, but it still won't make it illegal to bring children in for domestic labour."