I only see Gmail, Hotmail, Yahoo and CSV as the only options for the invite.

How do I get the others on there like Facebook?  I can't see any option to add providers although the ordering seems to be missing 1-3.

[edit]  in case anyone else is wondering, you need the social bridge plugin to get fb, twitter, and linkedin to work.  dont worry its free and the link is in the expanded description of this plugin.