When you hear of a celebrity who "dropped off the face of the earth," that usually means they stopped getting work, or fell out of favor, or maybe retired. This list means it literally, in that these people were rather well known and suddenly they disappeared even from their friends, family, and co-workers, never to be seen again. That doesn't mean the disappearance was a mystery, or is "unsolved." The sudden disappearance of Glenn Miller is pretty well established to be a plane crash at sea. The reason for the disappearance of a war correspondent can be assumed, even when no witnesses and no remains are found. But others are inconclusive- they may have been murdered, or they could still be alive somewhere, living under an assumed identity.
You would expect a list like this to have Jimmy Hoffa and Amelia Earhart, and indeed they are here. But you'll also learn about many celebrities whose disappearances flew under your radar, or were famous in another country, or who vanished a long time ago. Read about 30 of them at Bored Panda.