It's helpful, but only if you actually like using it as a social media.
If all you do is posting self promo for your comic... it won't convert non-readers into readers. Nobody wants to follow an account that posts nothing but promos for a comic they're not even familiar with.
But if you post your art, talk about your interests (bonus points if your interests are relevant to your comic in some way: e.g. "I love pirates!! Here's a cool random pirate fact!" kinda tweets by a creator who makes a pirate comic), make friends with other creators, over time that's going to help. It probably won't give you instant results, however. You have to actually enjoy doing this in order to stay in the game long enough to see meaningful results.
Also, you have to be genuine. Sometimes you see someone approaching people with the intention of using them for self promo. That's gross, and will backfire sooner or later!