There has been a Hibiscus thread on the Tropicals forum for a couple of years,
The thread "Hibiscus" in
Hibiscus forum It's not terribly active.
Just my opinion, but it seems the forums that are dedicated to one single type of plant seem to start and stop a lot. Why have a whole forum? Start a thread featuring Hibiscus on this forum, or even on the Indoor Plants forum or wherever else there might be people interested in Hibiscus.
Eg. there is a Brugmansias forum, and it is pretty much dead for at least half the year, despite the efforts of a few of us who grow them in Florida and California year 'round. Same is true for Roses, Iris, and many of the other forums that feature just one kind of plant.