Well, I am still using Google+ for social media, so Tumblr is going to outlast that at least. (sidenote: The shut down date for G+ has been moved up from August to April, so export anything you want to save quickly.) I have only begun to research G+ replacements like MeWe and Pillowfort, so I am not ready to comment on those.
Remember your demographic. You will want to go where your audience will be. If you are looking for a certain demo, you could even make TikTok work for you.
Most importantly, remember that social media is at best a back up. I have never known anyone to read a novel because he or she stumbled across a Facebook page. The general strategy is to engage first and then use social media to keep them engaged with you. Volunteer to be a guest for podcasters, YouTubers, local newspaper writers, and local radio show hosts. These people are almost always hungry for content.
Lastly, perform a publicity stunt. When the police march you away in handcuffs in front of the news cameras, remember to wear a t-shirt with the name of your book.
