If you are reading this report, may be that you are looking for this interesting OS X network application.
“Network Utility” was usually stored in “Utility” folder but for reasons that I don’t know, this application (like many others) is stored into another core system folder (see picture below).
In order to launch it, look at this folder
Macintosh HD > System > Library > CoreServices > Applications >
Many other OS X utilities are stored herein.
Another solution is to get to it with Spotlight by typing “Utility Network” in the search form!