FB quote :
You cannot: Condition entry in the promotion upon a user providing content on Facebook, such as making a post on a profile or Page, status comment or photo upload.
You cannot: Administer a promotion that users automatically enter by becoming a fan of your Page.
You cannot: Notify winners through Facebook, such as through Facebook messages, chat, or posts on profiles or Pages.
You cannot: Instruct people (in the rules or elsewhere) to sign up for a Facebook account before they enter the promotion.
3.6 You must submit materials for any promotion you plan on administering through the Facebook Platform to your account representative for our review and approval at least 7 days prior to the start date of such promotion. Promotions not approved in writing within such time period will be deemed unapproved.
For clarity, a "sweepstakes" is a promotion that includes a prize and a winner selected on the basis of chance. A "contest" or "competition" is a promotion that includes a prize and a winner determined on the basis of skill (i.e., through judging based on specific criteria). Publicizing a promotion on Facebook means promoting, advertising or referencing a promotion in any way on Facebook or using any part of the Facebook Platform.