What are the repercussions for knowingly harboring a runaway?

This is a very interesting question.  I am not certain my response is correct and look forward to the other CA lawyers adding their thoughts. 

If you daughter is an adult, there is nothing you can do.  Even is she is a minor, in the facts that you raise, I do not think you have any case or claim against the other family.  In any legal case where you are seeking damages from someone else, there are 4 questions we ask.  The first question is whether or not the other person owed you a duty.   Duty is a very difficult concept for us to describe.  There are so many cases on the concept and in many, even judges don't agree. As a simple example, court's have held that 2 participants in a sporting event do not owe each other a duty.   So if a runner is sliding into second base and gets hit in the face when the shortstop is turning a double play, the runner has not case against the shortstop - there is no duty.

In your case, I do not believe that the friend, his sister or the mother owed you a duty to disclose the location of your daughter, even if you ask if they know her location.  Simply stated, they owed you no legal duty of care.  Maybe a moral obligation, but no legal duty.