Trace lost post to find vehicle using tracks (11)
I believe the answer is:
caterpillar
'vehicle using tracks' is the definition.
(vehicle with caterpillar tracks)
'trace lost post' is the wordplay.
'lost' indicates anagramming the letters.
'post' becomes 'pillar' (I have seen 'Upright post ' mean 'pillar' so perhaps 'post' could also mean 'pillar').
'trace' with letters rearranged gives 'cater'.
'cater'+'pillar'='CATERPILLAR'
'to find' is the link.
(Other definitions for caterpillar that I've seen before include "Heavy tracked earth-moving vehicle" , "future monarch, perhaps" , "Tiny creature" , "sort of grub" , "8 17" .)