Armstrong was last seen at his home on west 25th Street in Merced, California on December 17, 1993. His girlfriend saw him before she left for work at 7:45 a.m. Approximately an hour later, Armstrong's brother stopped by his house and found it empty, but Armstrong had left his wallet behind. He was supposed to meet his girlfriend for lunch later that day but did not keep the appointment. He has never been heard from again.

Just two hours after Armstrong disappeared, his co-worker, Steven Lombard, vanished from Merced. His pickup truck was later found abandoned in a local K-Mart parking lot. The men were both employed as tow truck drivers for RTS Towing, but they were not close to each other and their loved ones do not believe they would have gone anywhere together. Investigators are unsure whether their cases are related.

Armstrong and Lombard are considered to be missing under suspicious circumstances; their cases are being investigated as homicides. Armstrong reportedly believed his coworkers were engaged in illegal activity at the time of his disappearance, and Lombard had a dispute with his boss on the day that he vanished. Armstrong's mother died in 2009, but his father and seven siblings are still alive. Both men's cases are unsolved.