Lookalike targeting is a form of audience targeting that uses lookalike audiences to increase your ROI. Lookalike targeting is used when you want to target an audience that is similar to your existing customer base.
To engage in this type of audience targeting, you first need to create a custom audience to tell Facebook what kind of users you’re looking to reach.
Lookalike audiences are those that are similar and/or replicate specific data from your existing customer base. Facebook takes your pixel data, app data or fans of your page and then identifies similarities of the people in it — hence the name “Lookalike Audience.” Some of the data they look to match up includes demographic information or interests.