Follow up on or go after (6)
I believe the answer is:
pursue
This clue is a double definition.
'follow up on' is the first definition.
(synonyms)
'go after' is the second definition.
(pursuing is a kind of going after)
(Other definitions for pursue that I've seen before include "Seek" , "Be engaged in - hunt" , "Search for" , "Chase, run after" , "Dog" .)