A family of seven are believed to have travelled to Turkey after going missing from their home in Bradford.
Imran Ameen, 39, his wife Farzana Ameen, 40, and their five children aged between five and 15 have not been seen since October 5.
Police believe the Ameens have travelled to Turkey, but their current whereabouts are not known.
Officers from West Yorkshire Police are now working with relatives in the UK as well as Turkish authorities to try to track the family down.
Assistant Chief Constable Russ Foster said a "primary concern" was the safety and welfare of the young children, and to ensure the safe return of the family to Britain.
Anyone with information on the Ameens' whereabouts is urged to contact officers on 101.