The national definition of a 'Missing Person' is 'anyone whose whereabouts cannot be established and where the circumstances are out of character or the context suggests the person may be subject of crime or risk of harm to themselves or another'.
This does not cover friends or family that you may have lost contact with over the years and you now wish to locate or make contact with. In these circumstances you may wish to consider searching on the internet or social media to locate them or employing a tracing agency to locate them for you.