Picture book character lost in a crowd (5)
I believe the answer is:
waldo
'picture book character lost in a crowd' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for waldo that I've seen before include "Gizmo" , "Ralph -- Emerson, US poet/essayist" , "name Emerson had" , "Low ad (anag) - boy's name" , "See 8" .)