@rich-brooks My general practice is sending a personal message to each as a start, and asking them if I can add them to my mailing list (or suggesting they sign up directly for something). It all depends on how I view them.
Now Twitter and FB present challenges, because I have to make a relatively quick decision whether someone is a prospect in target, a prospective partner or resource, or totally out of my ballpark.
Anyway, this starts a conversation, and based on reactions, I form next steps.