If you have serious concerns for the safety and welfare of a person, and their whereabouts are unknown, then you may immediately report them missing to local police by filing a missing persons report. You do not have to wait 24 hours to report someone as missing.
If you have lost contact with a family member over time however the person is not reported as a missing person to police, you may wish to utilise the services of a family tracing agency. Search agencies
are able to help people reach relatives and reunite families, often in times of special need.