these are book groups, not cover sites.

https://www.facebook.com/groups/science.fiction.publicity/?ref=br_rs
 
https://www.facebook.com/groups/booknest/?ref=br_rs
 
https://www.facebook.com/groups/scifipimp/?ref=br_rs
 
https://www.facebook.com/groups/438286272985158/?ref=br_rs
 
https://www.facebook.com/groups/thebookstopauthorsandreaders/
 
https://www.facebook.com/groups/topshelfmagazine/
 
 

https://www.facebook.com/groups/allthingsbooks/members
 
https://www.facebook.com/groups/2213398116/members
 
https://www.facebook.com/groups/315672875251373/members
 
https://www.facebook.com/groups/Bookorbust/members
 
https://www.facebook.com/groups/AllAboutBooks2009/members
 
https://www.facebook.com/groups/books45
 
https://www.facebook.com/groups/174224899314282/?ref=br_rs
 
https://www.facebook.com/groups/459702047562591
 
https://www.facebook.com/groups/639869959449405/members
 
https://www.facebook.com/groups/626706317815363/members
 
https://www.facebook.com/groups/1987913304858831/members