Vim show non-visible characters and look for whitespace or tab

vim_tab_space_check

:syntax on
:set syntax=whitespace

... then search for a string
...tab characters will be highlighted in blue
...space characters will be highlighted in red

If comparing more than one file in split windows, switch to that file (Ctrl-W w)
and set the syntax equal to whitespace to enable the color coding effect (:set syntax=whitespace).

# can be used to show all non-printable characters as ASCII characters.
:set list
:set nolist