Apple’s search tool, Spotlight, does not search every folder on your Mac’s hard drive. Apple configures it to skip some folders that it thinks you won’t want to search. For example, Spotlight doesn’t search inside the various Library folders on your Mac. If you’re looking for a font, such as Helvetica, Spotlight won’t find it for you.
I supplement Spotlight with a handy application named Find Any File which truly does search inside of all folders on your Mac. It’s not a fast as Spotlight, but that’s a worthwhile trade-off in my mind. Find Any File’s interface is based on Apple’s Find File which was part of older versions of the Mac operating system from the mid-90s, so FindAnyFile’s interface might look familar to long-time Mac users. It’s interface is easy to use, regardless.
It’s important to know that due to Mac OS X’s permission structure when you first open Find Any File it’s only able to search files that you own. If you want to search all files on the hard drive then hold down the Option key while clicking on its Find button. You’ll be asked for an administrator password and then Find Any File will restart with root permissions. This means that it’ll then be able to really find any file on your Mac’s hard drive.