I think it's outdated or was phased out.
Google's Android Device Manager works far easier, with your Gmail log in.
If you check in Security - Device Administrators to see if it is enabled. It usually is the default in recent Samsung's.
There should be a Device Manager app installed, though it's not needed. You can also type device manager in the Play Store app.
Give it a try from a pc.
www.google.com/android/devicemanager