Whereabouts Are or Whereabouts Is
Whereabouts Are or Whereabouts Is :
Despite the deceptive S on the end of the word, “whereabouts" is normally singular, not plural.
“The whereabouts of the stolen diamond is unknown."
Only if you were simultaneously referring to two or more persons having separate whereabouts would the word be plural, and you are quite unlikely to want to do so.
From Whereabouts Are to HOME PAGE