My infantry line company had just one MIA:
PFC Robert S. Trujillo, rifleman, was on a combat operation with his unit near the border of Quang Nam and Quang Tin Provinces in South Vietnam on January 7, 1968. During a fire fight with a superior enemy force, his battalion was forced from their position and began a breakout maneuver. Members of Trujillo's unit saw him stand up and start to advance with the armored personnel carriers (APCs) that were attached to his unit. That was the last time he was seen, and he was not wounded at that time. A search of the area was conducted on January 8 and again on January 16, but Trujillo was never found.
He was carried on the roster until the mid- 1980s I think and promoted to staff sgt, finally declared dead. Never found a trace or even anyone who could say he was no longer missing. It was A Co, 2/12 Cav, 1st Air Cav.
This web page lists all of the 12 Cav MIAs.
12th Cavalry MIAs