10,000 unaccompanied children unaccounted for - EU police agency
Authorities dealing with Europe's migrant crisis have lost track of around 10,000 unaccompanied children over the last 18 months.
The European Union police agency announcement comes amid fears that organised crime gangs are beginning to exploit the vulnerable youngsters.
Europol Chief of Staff Brian Donald said the figure "would be a conservative estimate across all the countries that are dealing with this migrant crisis".
The revelation that so many youngsters are unaccounted for is the latest worrying development in the migrant crisis and underscores the risks faced by people fleeing conflict, poverty and persecution in the Middle East, Africa and Asia once they have reached the apparent safety of Europe.
Mr Donald said the estimate of 10,000 missing was based on reports by law enforcement authorities, governments and non-governmental organisations.
"They're lost in the system," he said of the minors. "I think our concern is that we know that there are people out there who will exploit minors. We know there are people who will take them and use them for their own purposes."
The Stockholm county government released a report last week citing Swedish Migration Agency statistics that said 1,900 of the 55,000 unaccompanied minors who have applied for asylum in Sweden in the past six years disappeared. The whereabouts of 1,250 of those is still unclear. About 88% of those who went missing are boys.
"There is very little information about what happens after they disappear. These children are particularly vulnerable to being exploited in various ways," the report said.
Amir Hashemi-Nik of the Stockholm County Administration said some of those who disappear are believed to be in the grip of human-trafficking rings and end up in prostitution, begging or other criminal activities. Some disappear simply because they do not like the place where they have been assigned and decide to leave, others go when they approach their 18th birthday because they are worried it will be harder to get asylum.
North African boys are particularly likely to go underground because, unlike Syrians or Afghans, they are unlikely to get asylum.
"Many of them have lived on the streets in many other countries before coming to Sweden," the report said. "Many of these children become involved in crime."
Europol analysts studying law enforcement details from across the 28-nation EU are concerned that they are beginning to see cross-pollination between people-smugglers and criminals who traffick and exploit humans.
"That confirms our understanding of criminal organisations at the European level," Mr Donald said. "They are very adept at making changes to reflect the current situation. So if the market for them is changing then they will follow that market and at the moment the area of exploitation that's largely available is the exploitation of migrants."
Of the 150,000 migrants and refugees rescued at sea and taken to Italy last year, 12,360 were accompanied minors, according to the UNHCR office in Rome.
UNHCR spokeswoman Carlotta Sami said there is no firm figure on how many of those have slipped away or might have been exploited.
Save the Children Italy spokesman Michele Prosperi said that Europol "sounded an alarm that is based on a real risk" because thousands of minors do not stay within the system of migrant protection.