The EU's agency for law-enforcement cooperation says at least 10,000 unaccompanied migrant children have vanished after registering with state authorities in Europe over the past two years.
"Not all of them will be criminally exploited; some might have been passed on to family members,” British newspaper The Observer quoted Europol's chief of staff Brian Donald on January 31 as saying. “We just don't know where they are, what they're doing or whom they are with."
Donald warned that a sophisticated pan-European “criminal infrastructure” was now targeting refugees.
The international children's charity Save the Children says about 26,000 child migrants arrived in Europe in 2015 without any family.
There are fears unaccompanied children and young people may be dragged into sex work and other illegal activity.