I have not had much luck with Facebook, and here is why.
Facebook demographics statistically speaking is older. So first before you advertise anywhere you have to figure out your demographics, and your target audience.
Instagram can help you figure out your demographics, but you have to change your account to a business account. Then I think at 100 followers it will start showing you the people that a following you, their age range, gender, and region.
When you are looking at hashtags there are two tabs, the popular tab and the new tab. Make sure you look at the new tab, that is most likely where you are. Don’t over use one hashtag, if every post you make is #webcomic, Instagram will think you are a spammer.
Also the whole point of social media is the interact. If you want followers you have to follow people. If you want comments comment on other people’s work. And don’t just comment on the popular art, you won’t get noticed. Find other artist just starting out and build an online support group. A lot of the artist here on tapas actively like and comment on one another’s insta post, to help boost ourselves up on the algorithm.
Also try some # DIYS, it gets attention on your work by drawing someone’s character. This time do try to find popular artist and see if they have a DIYS to participate in.
That’s all the tips I have. Oh and don’t just do comic related posts, treat Instagram like a small art portfolio and show off all your work. If you want to connect on Instagram I am always open to more artist friends on there, you can find me @gabbiewolfcomics