Despite the deceptive S on the end of the word, “whereabouts” is normally singular in meaning, not plural, because it means “location.” However, it is commonly used with a plural verb: “Its whereabouts are unknown.” But the Associated Press prefers a singular verb: “Its whereabouts is unknown.” Many authorities disagree, and most will accept either form. Of course if you were simultaneously referring to two or more persons having separate whereabouts it would require a plural verb: “The whereabouts of several members of the team were unknown.”