If you are using a version of Microsoft Windows you get some information on Using the "A word or phrase in the file" search criterion may not work . The point is: the operating system looks for the search string only in certain types of files. To enable it to check your *.ino files as well you have to use regedit.
Whenever you use regedit take care. Strange things might happen when you make any mistakes. So be warned.
You have to enter a new key "*.ino" in the section HKEY_CLASSES_ROOT and add a subkey called "PersistentHandler" . There you have to insert the string
This is also valid for Windows-7:
If you also handle old sketches of the *.pde type do the same with "*.pde".
You can also use the grep.exe which was shipped with the early Borland Pascal system if you know how to handle a command line.