It has been a quarter of a century since the 20-year-old mysteriously vanished without trace, but his parents continue to push for information. — It was the spring of 1997, and 20-year-old Gregory Keith Mann Jr was busy enjoying life on an evening out with his friends. He was a successful car salesman and was about to move in with his fiancee, so there was much to look forward to. However, little did they…