Please note that providing an entry into a giveaway for sharing a post or commenting on a wall on Facebook violates the Facebook promotion guidelines. For this reason we have not integrated a 'Share' option yet. Full details on Facebook Guidelines: https://www.facebook.com/page_guidelines.php
Facebook Guidelindes: "3. Promotions may be administered on Pages or within apps on Facebook. Personal Timelines must not be used to administer promotions (ex: “share on your Timeline to enter” or “share on your friend's Timeline to get additional entries” is not permitted)."
As an alternative, many PromoSimple users utilize the 'Custom Congratulations Message' area, which can be accessed on step 3. Display for Business and Brands & Agencies accounts, to encourage commenting or sharing on Facebook (this is not in exchange for additional entries). This area is customizable with HTML, images, widgets, etc.
The Refer a friend entry method does include a Facebook Share button. This is allowed because the entrants are not receiving additional entries for sharing the giveaway. Entries are awarded only when new users enter the giveaway within the entry form. The Refer a friend option is available for Business and Brands & Agencies plans.