Hey abdolrahman kiany!
Thanks for your question. POST doesn‘t necessarily imply that the endpoint needs to return something. It merely implies that something is written or changed instead of read.
So in your case (following a user) I‘d go with something like.
POST /users/{id}/follow
POST because something is WRITTEN (e.g. following a user, which triggers a change in your database){id} of the user that is subject to be followed- And then
follow to explicitly specify the action
Of course it depends a bit on your current structure, but something along those lines should work just fine.
Hope that helps – reach out to me via Twitter (@rbluethl) if you need any more help.