What matters is the keywords that you use--hashtags are fine if it's a hashtag that people are actively searching (so they may indeed be searching generic hashtags like #webcomic or #tapas (as well as seasonal ones like #inksgiving , which recently ended, but there's also #freecomicsday which is...not exactly about webcomics but a lot of people put their comic on there, so keep an eye out for when certain hashtags blow up--which isn't as often for comics as it is for illustration, but things like #portfolioday include comic work that you would consider portfolio worthy)) Like yes, hashtags will effect how many people will see your post, but if they're searching in the tag anyway it does not matter.
So think about what keywords people would be searching outside of hashtags, words like "romance comic" or "gag comic" or "weekly comic" or "webtoon" (even if it's not on webtoons, a lot of people do not know that there's a difference) or "just updated" and make sure those words are naturally in your tweet. Don't just drop a link and a hashtag and run.