Find Logged in User on netowrk PC

Does anyone know if there is a way to find the PC name that a user is logged into on a Netowrk. 
 
I used to use net send & netstat but after they disabled the messaging service by default I have not been able to use it. 
 
for example I would like to enter a username and it will display PCName that a user is looged into.
 
If possible without searching all PC's on the network (that would take too long)
 
Thanks
 
Ralph

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