Missing persons

Questions:

• Do I have to wait 24 hours before I can report a person missing?
• How can I trace a missing relative with whom I have lost contact?
• I have not seen my neighbour for a few days and there is milk on the doorstep, what can I do?
• I think that my friend/relative is in prison, but I am not sure and I do not know which prison, what can I do?