Almost 20% of unaccompanied child migrants from Albania taken in by Kent County Council this year have disappeared, the BBC has found.
The local authority took in 197 Albanian children up to 31 October, 39 of whom have gone missing.
Ecpat UK, which campaigns to protect children from exploitation, said the figures were very concerning.
The council said it had worked closely with the Home Office and police to safeguard vulnerable children.