Someone who has disappeared for a long period of time,commonly with no known reason is usually classified as a/an:

Question

Quizplus · Accepted Answer

A lost person implies that they are physically lost or disoriented in a specific location. An abducted person implies that they were taken against their will by another person or entity. A missing person is the most appropriate term for someone who has disappeared for a long period of time, commonly with no known reason, as it covers all the possible reasons for their disappearance.

Someone Who Has Disappeared for a Long Period of Time,commonly