was moss steiger ever a character on wkrp in cincinnati and did anybody ever see him?

Moss Steiger was WKRP's late-night DJ (he did the thankless shift between midnight and 6 a.m., known as the "graveyard shift"). He was never seen. In "Johnny Comes Back," Johnny fills in for Moss (who is called "Steiner" rather than Steiger here), and we learn that Moss is suicidal:

JOHNNY: What happened to Moss?
LES: He tried to kill himself again.
VENUS: This time he got in the closet with a Hibachi and tried to asphyxiate himself.

Moss is mentioned a couple of other times in the series: In "Filthy Pictures," after the botched burglary, Johnny goes into the booth to "see what Moss is up to," and at the beginning of "Nothing To Fear But..." Johnny is filling in for Moss.

In an episode of "The New WKRP," Moss dies in a freak accident and Johnny takes over as late-night DJ.