I know there were plenty of processes to deal with crimes, to varying degrees of effectiveness, but what about disappearances? If you were, for instance, a mother in London in 1823 and your son left in the morning and didn't come back, what would you do to find him? Were there any organisations or groups or processes to help you? (I'd love to hear about processes anywhere and anywhen, not just London, 1823.)
While answering a different question a while back, I found this story, which happened in the mid-1500s, about the disappearance in France of a wealthy Italian merchant from Lucca. The way it was eventually solved is a little bit fanciful, but it shows how a missing person investigation - in this case an international investigation since it involved Italy, France, and England - could be handled by the authorities during the Renaissance.