@enad12 – I suggest looking at the plugins in the wp-repo and see if any of them may suit your needs.
https://wordpress.org/plugins/search.php?q=invite
https://wordpress.org/plugins/search.php?q=facebook
I myself avoid adding anything facebook to any of my sites as much as possible. In the very few places that I did add anything fbook, I would make sure that they loaded all assets from my site and not a third party server – for site speed and privacy issues as well.
for example the “2 Click Social Media Buttons” plugin requires a double click in order to turn on these third party integration / sharing things – and the author has a write (in German that may needs translating) on his site – which is linked to in the plugin descript – that describes some of the laws in Germany and Europe in regards to leaking user info to third parties – so if you are going down that road I would look more into that and whatever laws you may need to follow in your area of the world in regards to those kinds of things.
