Facebook became an issue for me too. I worked for years to build up the audience on my FB author page. Around 2012 Facebook change their algorithms and my post outreach dropped dramatically. This use to bother me tremendously but, after a year on Steemit, I don't care about Facebook much anymore. My strategy has been to "boost" FB the occasional post asking my audience to sign up for my email mailing list. This way you can connect with your audience directly via email. It's worked quite well.
I like your thinking here! Maybe in a few months, I will start to forget about FB and focus solely on Steemit. But at the moment I can't quite bring myself to walk away from years of work on FB :-( Congrats on the book launch BTW, you must be thrilled !!
I was sad to leave my audience on Facebook. I kind of feel like we grew up together. Lol. I still do the occasional targeted "boost" but that's the only way they allow my audience to see it. Thank you! I am thrilled beyond belief. It started off slow the first day but it's selling very well now! I have a second novel to finish this summer and then I'll be taking about a month's break to just travel, take photos, and write posts.