Leading celebrities plump for one who is no influencer (8)
I believe the answer is:
fatalist
'one who is no influencer' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'leading celebrities plump' is the wordplay.
'leading' means one lot of letters go next to another.
'celebrities' becomes 'a list' (A-list).
'plump' becomes 'fat' (similar in meaning).
'alist' after 'fat' is 'FATALIST'.
'for' is the link.
Can you help me to learn more?
(Other definitions for fatalist that I've seen before include "doom merchant" , "One who accepts events as inevitable" , "One submitting to destiny" , "Predestinarian" , "One believing in predetermination" .)