If they don't want any contact it will be difficult as I don't think there is any way you can find out for them. The easiest way would be for them to ask their bishop to request their record (they can look up their ward in the "find a meetinghouse tool" from the church web page and get the bishop's phone number from there). If they are baptized, a record will come in. They can then, at that time, speak with the bishop about how much contact they do or do not want (or start the process to resign their church membership if that is their preference).