Can I ask the referee for help? I recently submitted a manuscript, and the referee's response is that I did not discuss one aspect of the theory I am interested in. This is true, because I am new to this topic, so I missed that aspect. 

I am wondering if I can ask the referee for help point out some references or even discuss with him/her. Is it OK?
I see no problem with asking the referee (via the editor) for relevant references. The referee is under no obligation to reply, but I don't think it's wrong to ask.  But I don't think you should ask to communicate directly with the referee.