Simmons was last seen at a Grateful Dead concert at Carter-Finley Arena at the University of North Carolina campus in Raleigh, North Carolina on July 10, 1990. Simmons told the friends he accompanied to the concert that he was leaving the arena and heading to the parking lot to the car. He never returned. Simmons was carring a small gold rectangular keychain with his initials "DSS" at the time of his disappearance.

Simmons and his friends were students at the University of Western Florida at the time of his disappearance. They had driven to North Carolina to attend the concert and planned to head back to their own campus afterwards. Simmons's friends called his father and told him they could not locate his son, then proceeded back to Florida. Simmons's father drove to North Carolina four days following his son's disappearance on July 14, 1990. He filed a missing person's report with authorities at that time.

A witness came forward the week following Simmons's disappearance and stated that she spoke to a man who fit his description near a rest area in New Jersey on July 16, six days after the North Carolina concert. The witness said that the man appeared disoriented and did not remember his name, but he stated he was from Florida. The witness left the unidentified man for a moment to locate a police officer across the street; when they returned, the individual had left the scene. Authorities are not certain if the unidentified male was Simmons.

Simmons was carrying a small gold rectangular keychain engraved with the initials "DSS" at the time of his disappearance. His case remains unsolved. Florida and North Carolina police are investigating.