I’m pretty sure that is completely against Facebook terms of service. They’ve blocked Google from accessing your contacts as well as other services. They do not want you stealing your friends away from their advertisers.
This may help with getting users to invite https://buddypress.org/community/groups/invite-anyone/
Good mod modemlooper posted there and I use it too. I think it’s got some premium features for Yahoo integration too etc…
I’ve found one service that can compile all your friends emails from facebook and once you have that list you can do what you like with it.
You can always create an event page on FB, invite all your friends there and in the event page you post your website URL inviting them to your site I guess..
Thank very much both of you. I greatly appreciate your time in helping me resolve this