Neon the Unknown appeared in issues #1-17 of Hit Comics (published by Quality Comics) in 1940-1941, occasionally even rating the cover of that series.
from Hit Comics #9 (March 1941)
cover by Lou Fine
When he appeared in a DC comic book, it was in All-Star Squadron #31-32 (cover-dated March 1984 and April 1984):
Unfortunately, it was as part of a group of superheroes that would be killed off shortly after they first appeared.
He was also included in a group shot with various WWII-era superheroes in History of the DC Universe:
More about who he was and how he got his powers in another post . . .