Occasionally witnessed teen's grim need for something to drive (6)
I believe the answer is:
engine
'drive' is the definition.
(thesaurus)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for engine that I've seen before include "turn of mind once" , "Motive machine" , "Machine with moving parts" , "Locomotive" , "machinery" .)