In a nutshell; put yourself in the position of the person who is seeking the missing person, yourself as an investigator and finally the person who is being sought after.
Three people; three different agendas. Imagine you as each of them, as well as their agendas. Quite a few scenarios will pop up, however, I believe the most important one is, "Once I have located the missing person, what can I (as an investigator) do next - e.g. legally, morally, ethically."
I do hope that very soon I will be elaborating further on this subject of locating persons and if it comes to fruition, will post on this forum.