There are three types of audiences you can custom target:
The customer list is interesting since you can upload a list of emails or names and phone numbers. This means that you could potentially show your Facebook ad to everyone who came to your race last year and their friends. A word of caution, though. We have heard that this may not yield the kind of results you expect since the email address or phone number people use to sign up for a race may be different than the one they use for their Facebook account. This of course means the “yield” may be disappointing. Also, the Cost per Click or Cost per Impression may be high (a common frustration with Facebook since they do not give you specifics of how many impressions or clicks you get for your money – just approximations).
Let us know your results if you experiment with this!