"Buckwild" Star Shain Gandee was found dead in a vehicle in West Virginia this morning ... 31 hours after the 21-year-old MTV reality star had been reported missing, this according to law enforcement.

According to officials, Gandee -- along with 2 other bodies -- was discovered in the vehicle in Sissonville, West Virginia.

As we previously reported ... Shain was last heard from around 3 AM on Sunday morning, when he and his uncle David Gandee told people they planned to go 4-wheeling.

It's unclear if 48-year-old David was one of the deceased people in the vehicle where Gandee's body was discovered.

Story developing ...