This always has mixed results, since people on Facebook don't know anything about book cover design, they probably aren't your target market, they probably aren't
ideal readers of your genre, and they aren't designers.
Not exact matches
You want about 5000 downloads
of ideal readers in your
genre.
In fact, the creation
of a central blog as main linkage point advertising
genre / author listing / images would be
ideal for referring interested
readers, plus links to Youtube book trailers!
One
of my favorite ways to find key hashtags that your
ideal reader uses is to look at what hashtags other successful authors in your
genre are using.
basically, you kind
of have to guess at who your
ideal reader is, initially: what's your
genre?
You can use gut feel here, according to where your
ideal readers hang out, the nature
of your books, and things you've heard are effective for other authors in your
genre.