RunSignup offers several reports that make the process of creating a Facebook Custom audience from your participant lists a snap. In total, three reports have been made available for easy download: All Participants, Current Participants, and Non-Registered Previous Participants. These reports contain all the information RunSignup has available that Facebook can use to create a Custom Audience, and have been pre-formatted for easy importing into Facebook.
For more details on how to leverage all of the options, check out our RunSignUp & Facebook Custom Audiences blog post!