A writer promotes to writers
Most writers promote their books to other writers on Facebook groups. There are even groups only for promoting books… and all the members are writers. Why?
Of course the writers are also readers and buy books, but they are, like most readers, highly specialized. I’ve noticed lately a lot of romance books being promoted (no comment on the tacky covers). The copy/paste action in a writer’s group is a waste of time and energy you will never get back. Total waste. Mass marketing like this is expensive even if you don’t realize now.
The writers with a large base of reader who can help you promote your book will do so only if you are their friend and even then only if their readers are interested in the respective genre.
Take a hint! Focus! Find your readers group based on their interest. It might be helpful to promote your romance group on a Facebook group of chocolate and wine lovers.