Same issue here. I click on "Use Facebook App as Admin" and... nothing happens.
It would be helpful just to know what's SUPPOSED to happen. The instructions on the Social tab aren't at all clear about that, which makes troubleshooting pretty difficult.
I'm also experiencing the problem of Facebook being unable to display any og:images. My featured images and post images are all large enough and always listed when I run the debugger... but they simply won't display. I have a default image url set on the Social tab, but that image doesn't even show up in the debugger list.
Given how common both of these issues seem to be, the near complete lack of documentation is frustrating and a little disappointing.
http://artieandgilda.com
https://www.facebook.com/artieandgilda