Simple:
* The police are investigating the whereabouts of the missing child.
* I have no idea of his whereabouts.
* Her whereabouts are unknown.
With more context:
* The detective was determined to uncover the whereabouts of the stolen jewels.
* The hikers were lost, and their whereabouts were a cause for concern.
* After the storm, the ship's whereabouts remained a mystery.
As a question:
* Do you know the whereabouts of the library books?
* Have you any idea of the whereabouts of the missing dog?
Remember that "whereabouts" is always plural and refers to the place where someone or something is.