1. Enoch: Genesis 5:24 And Enoch walked with God; and he was not, for God took him.
2. Elijah: 2 Kings 2:11 Then it came about as they were going along and talking, that behold, there appeared a chariot of fire and horses of fire which separated the two of them. And Elijah went up by a whirlwind to heaven.
Bingo! This Earth that God created has its mysteries. I do believe in UFO because the Bible speaks of them or shall gives hint to them. As for people disappearing, can it be God giving us a glimpse of what the rapture will be like. Imagine millions instead of 1 person just poof off the face of the Earth.
These people who disappeared in the past, they did not die neither they simply vanished into thin air. The Bible does states that when the rapture occur, we will not die but to be united with those in Christ in the air in a TWINKLING OF AN EYE.
There are several odd scenes int he Bible which hint strongly of a parallel where/when un detected by our sense (see Daniel chapter five, for starters).