Yes, you would have to create test-accounts for the reviewers to use, and you would have to provide the login in the reviewers comment-section when sending. It would also be smart to fill them with other fake friends before you send them so it's not completely empty, I.E yourself, especially if you don't have any automated events for situations where no one else is using the app.
If your app isn't depending very much on what's actually on the account (I.E friends etc), then sending fake facebook-accounts is probably not necessary, but since you state that friends and their behavior matter, then you should fill up some fake friends with some dummy data, and maybe use it yourself.
This is documented somewhere, and I believe itunesconnect at one point asked me if I had provided user-credentials if I had such an app.