I doubt going the Facebook App route will help too much unless it's finding friends that already use your service. The API only allows you to pull a list of friends that are also users of your Facebook App. Since the upgrade to Graph 2.0, you can no longer pull a complete list a Facebook user's friends anymore.
If there's value to members sharing content from your site back to their other social media accounts, that might be a possible route. That was a key part of Instagram's growth... people starting seeing photos from their friends shared from Instagram, encouraging them to create their own accounts.