Facebook has 2.80 billion monthly active users, 1.84 billion users that are visiting the social networking site on a daily basis. Your Facebook Group will likely be one of your biggest assets, and those followers, like those superfans on your newsletter, will happily one-click your latest release.
I can help moderate your group, deal with engagement (be it welcoming new members or making daily postings), to even coordinating parties with other authors and PAs.