In facebook you can leave a comment, or click on the share and it will give you an option to share the picture with public, family only, friends only... etc.
I don't think the share in FB has anything to do with the 'likes' you get on your FAA site.
When you're in FB look at the bottom of the picture and it will give you options there, as well as share.
Welcome to FAA and good luck to you.