I remember a segment where a mother kidnapped a child from his father and they got involved in a religious cult. I remember that the father was travelling around trying to follow the cult, but whoever he would talk to would start ranting and raving and never give him any information about where his ex-wife or his son went. The segment is similar to the Bill Day story. Does anybody remember what I'm talking about?

I remember Stack using the word "proselytize" in this episode. Hope that helps, lol.

I believe you're referring to the segment about Arthur Koropolous and his son, Nicholas. Here is the Unsolved Mysteries wiki link:

http://unsolvedmysteries.wikia.com/wiki/Nicholas_Koropolous

Yeah I think about this case a lot. Nicolas would obviously be an adult by now and I wonder if he has had any contact with Levia, While I'm glad that Arthur got his son back, I do feel somewhat sympathetic towards Levia as I don't view her as much as a criminal as a woman who was extremely confused as to her religious beliefs and was easily swept up (and allowed her son to be swept) up by the cult scene. I wonder if all these years later if she has re-established a relationship with her son?