(AFP) - Over 10,000 unaccompanied migrant children have disappeared in Europe, the EU police agency Europol said on Sunday, fearing many have been whisked into sex trafficking rings or the slave trade. Europol's press office confirmed to AFP the figures published in British newspaper The Observer, adding that they covered the last 18-24 months. The agency's chief of staff Brian Donald said the vulnerable children had disappeared from the system after registering with state authorities following their arrival in Europe. "It’s not unreasonable to say that we’re looking at 10,000-plus children," Donald said, adding that 5,000 had disappeared in Italy alone. "Not all of them will be criminally exploited; some might have been passed on to family members. We just don't know where they are, what they’re doing or whom they are with." Donald said there was evidence of a "criminal infrastructure" established over the last 18 months to exploit the migrant flow.