I don't think it's a problem with the social plugin. please enter the profile https://www.facebook.com/michael.kamleitner for testing purposes - everything's fine here.
If I open the profile url of John Smith I'm getting an error ("Page not found") - so imho the profile is restricted/not public at all. If it's privacy restricted, you can't use it for the follow-plugin. If you have access to John Smith's account, please double check his follower-settings: https://www.facebook.com/settings?tab=followers