My approach with social media is to interact with the readers I already have. I do it mostly to procrastinate from my writing. It's an escape. It's the only socializing I get outside of my wife, and she gets sick of me.
I'm such a huge fan of fan fiction, to me it's a great way for readers to become writers. It's like putting the training wheels on for writing.
Honestly, I don't think I'm a good promoter. I spend almost zero time or effort asking new readers to sample or purchase my work. That's not the job of the author. We should write our best material and leave it up to readers to spread the word.