Despite the misconception that you need to wait 24 hours, most law enforcement agencies advise people to report a missing person as soon as possible. You should call the non-emergency police number to file a report (unless you suspect foul play). If the missing person is a child, you should call 911 then the National Center for Missing & Exploited Children.A missing person is usually defined as someone whose location is unknown, and who therefore cannot be confirmed as alive or dead.