Since network prefs apply across different user accounts, they have to be stored in the base Library. Try these files:
Mac HD/Library/Preferences/com.apple.networkConfig.plist
Mac HD/Library/Preferences/SystemConfiguration/NetworkInterfaces.plist
Mac HD/Library/Preferences/SystemConfiguration/com.apple.nat.plist
Mac HD/Library/Preferences/SystemConfiguration/preferences.plist
The last one may delete a few prefs that are not network-related.