some other hashtags i've seen used apart from the ones mentioned include #digitalart or digitalartist, artistsontwitter, character design, and really lots of others it's simply a matter of finding out which ones suit your project. I've also noticed that some artists, if they're able, will participate in monthly challenges when they are held. Like last month was #AdventureApril and this month lot of people have been taking part in #MerMay.
Boiling it down it's a matter of finding niche groups and staying active, participating where you can and when you can to try and get eyes on your comic/social media. For some they manage to blow up but in most cases it's a bit of a slow start but once it starts gaining momentum thing begin to grow steadily it's just a matter of consistency