Personally, I hate Instagram nowadays and I quit Facebook a couple of years ago for the same reasons that I currently don't like Instagram. It feels harmful to my self-worth in all honesty. I have no idea how people get a following or "likes" or any of that. I have tried, and I have even sold work to some of my collectors there, but they were already my collectors before Instagram was invented. If they were inspired by my recent posts to buy something, maybe that was the case, but I have no idea. Either way, I am debating on if it's worth it to stay active there, so I agree with you.
I like your idea of wheat-pasting copies of the drawings around town without your name on it, but following it up somewhere on line with your name might be wise for people to connect the drawings to you.
I have a website, so I recommend that, and building a mailing list to send out news and new art every so often. You can get creative about what you send to them. It can be anything you dream up.
With your own site, you have a home base for which to email whomever you want to solicit to look at your work for whenever/whatever you want--galleries, collaborators, projects, other artists, municipal establishments (for murals, etc.), or whatever else. You can always usee the link to your site in your emails or even on a biz card/mail promo, stickers, anything...