How long must a person be missing before you should call the police?
Depends on the circumstances. Go with your gut on this one -- don't hesitate to call now if you feel something is amiss
There is no time limit but, it is determined by condition of disappearance. For an adult you can call immediately you feel he or she is missing. Go to this link for more details http://www.ehow.com/facts_7453089_long-police-obligated-look-them_.html.
U can all whenever u want. But I think they put a 24 hour hold on the call befor they classify the person is missing and start searching