There is already one! look on http://buddypressdev.org/plugins/
there, there’s one called Invite Friends click on it & download it..
For facebook it will be realease next week.
but i have some bug with it
Urgent! We really need an inviter plugin for BP 1.2+. It’s the most effective way to populate a community website, and is used by all community sites worth their salt.
It’s something I’m asked constantly about. we need a simple ‘Invite friends’ email function for members to use.
The “invite friends” plug in sounds great but will not work on wp3.0 BP 1.2.
The Invite Anyone plugin by @boonebgorges is great for inviting people but you have to enter their emails: http://teleogistic.net/code/buddypress/invite-anyone/ People on my site like it because they invite people who they know will contribute to the site instead of just click around.