In order to help you avoid a nasty lawsuit, it's against the Facebook Terms Of Service to require sharing a post in order to gain entry into a promotion:
https://www.facebook.com/page_guidelines.php
Quote:
|
3. Promotions may be administered on Pages or within apps on Facebook. Personal Timelines and friend connections must not be used to administer promotions (e.g. "share on your Timeline to enter" or "share on your friend's Timeline to get additional entries" and "tag your friends in this post to enter" are not permitted).
|
This is not permitted. If you're going to have a give away, entry must be available without sharing or liking the post.
