How can I target people who like my Facebook Page?
Target your ad to people who currently like your Page using connections targeting. In the targeting section, scroll down to Connections: Target people who are connected to. As you begin to type the name of your Page in the field, the names of Pages and other eligible content you manage on Facebook will show. This targeting is useful when you’re trying to reach the people who like your Page to show them special offers or new products.
This targeting option can also be used to reach members of a group you manage, or people who have joined your Event or installed your app.