The ship returned on August 18, 1590, only to find Croatoan carved on a post
The Lost Colony
Okay there are lots of theories what happened: Abducted by aliens?, The Lost Colony of Roanoke, and the Mysterious Lost Colony
Wilder theories aside, and given no bodies were found, the most probable is the most likely: They were attacked by a nearby tribe. They had valuable things (like metal) the tribe would want. Tribes often attacked other groups. Either the colonists were all killed, or the natives killed the men and took the women as captives.