Facebook Lookalike Audiences

How Facebook creates Lookalike Audiences

• In order to create the Lookalike Audience, the source Audience must have a matched count of at least 100.
• Facebook evaluates profiles for matched Audience members with their own proprietary algorithm, and based on the evaluation, Facebook populates the Lookalike Audience with other Facebook users that are considered similar to the original Audience members. 
• Lookalike Audiences can be optimized for reach or similarity. Optimizing for reach will return the top 5% of users with similar interests whereas optimizing for similarity will return the top 1% of users, those most similar to the Audience members.