Actually, that function has two strings: HL2Player.SprintNoPower and HL2Player.SprintStart.
However, if you have a function that is really difficult to find, you can try running these scripts:
https://github.com/Ayuto/discover_winIt first starts with simple string match searches (functions that have the same strings in both databases are renamed). Then it searches for all functions that only have one unnamed xref_to or xref_from function left. Those are easy to find. After that it repeats the steps again, because the string match search is now able to find new results. This is running in a while loop until no more results are found. If I remember correctly, it is able to find 8-12% of all functions, although it is in a very basic state and could possibly be improved a lot.
After running these scripts it's a lot easier to find other functions by finding/renaming global pointers, comparing the code (a decompiler helps a lot), function size, renaming the functions in a vtable or marking multiple functions as "possible findings". Generally speaking: the more you discover, the more it will ease finding other functions.