Moncer was last seen on February 18, 1982, leaving his residence in the 65000 block of Indian Run in Bellaire, Ohio. He has never been heard from again. He left behind his cigarettes, which is uncharacteristic of him. Two days after his disappearance, his wife found his gray Dodge Aspen idling in a ditch at the entrance of Anco Mining Road. The car was mud-splattered, the keys were in the ignition, the driver's side door was open and the dome light was on, although very dim. Moncer's coat, cigarettes, lighter and some change were inside the car. The interior of the vehicle was muddy and there were indications that a struggle had taken place.

Shortly before he vanished, Moncer had gotten a note in his mailbox made of letters cut out of a magazine. It said, "Leave It Alone, Or You Are Dead." He was unconcerned and threw it away. The person who sent the note has never been identified and it is unknown whether the note has anything to do with his later disappearance.

At the time he went missing, Moncer was working three jobs. He and his wife, Irene Zimmerman, were in the process of a divorce in 1982. He drank heavily, was having an extra-marital affair and had a bad temper, and occasionally beat Zimmerman as well as his girlfriend. Zimmerman stated he was overprotective, didn't want her or their three-year-old daughter to leave the house without him, and didn't want their pictures taken.

There were reported sightings of Moncer in the months after his disappearance. Zimmerman said she and their daughter were followed by a man in a truck for months after Moncer vanished, and for two years afterward, a man would hide in the shadows outside the house. Zimmerman believes the individual may have been Moncer himself, wanting to see his child. Zimmerman also stated she received several anonymous calls. One caller told her Moncer was dead and his body had been dismembered. This information has not been verified.

Moncer was declared legally dead in 1988, and his mother collected his life insurance policy. His police casefile was lost, but it was later located and the investigation was reopened in November 2007. His case remains unsolved.