How do you plan to monetize the social network?

If you have something people have to pay for, trade it for referrals.

If you don't, consider trading "X days ad-free" in exchange for referrals.

If you don't have a revenue stream from users or ads, focus on delighting people and offering an easy way to share after they've just gone through an experience that will make them think, "Holy shit that was awesome."

Good luck!