Appearance of people informally mentioned (5)
I believe the answer is:
guise
'appearance' is the definition.
(guise is a kind of appearance)
'people informally mentioned' is the wordplay.
'people informally' becomes 'guys'.
'mentioned' indicates a 'sounds like' (homophone) clue.
'guys' is a homophone of 'GUISE'.
'of' is the link.
(Other definitions for guise that I've seen before include "Shape; pretence" , "Mask" , "Show" , "Demeanour" , "Appearance, semblance" .)