Targeting Facebook Page Engagers is another way to target fans. Engagers include everyone who's visited your page, or engaged with your page’s content and ads on Facebook or Messenger. Actively interested in your work and engaging with your content on social media, Engagers simply have not “Liked” your page on Facebook yet.
To Target Facebook Page Engagers, first, insure that you have Page Advertiser or Page Admin access to the Facebook Page of the brand.
You can then target the engagers in the service by clicking on “Add New” or “Change Template,” followed by “Facebook," then “People Who Engaged With Your Page,” and selecting your page in the “Template Options” section: