Dairy product identifies missing person? (13)
I believe the answer is:
butterfingers
'missing person?' is the definition.
(a clumsy person who drops or 'misses' things)
'dairy product identifies' is the wordplay.
'dairy product' becomes 'butter' (butter is a kind of dairy product).
'identifies' becomes 'fingers' (finger can mean to identify a criminal).
'butter'+'fingers'='BUTTERFINGERS'
(Other definitions for butterfingers that I've seen before include "Someone always dropping catches" , "Person continually dropping things" , "Clumsy type" , "Someone who drops things" , "A poor catcher" .)