[Q] How do I find a device's location if I don't have access to it? topic

So I just noticed recently that a new device has shown up in my Android Device Manager. It is a Samsung SM-G900F, which apparently is a T-Mobile Galaxy S5 (it says T-Mobile in the web version of the Play Store). I only know two people with S5s and they're both on Verizon. I'm concerned someone has gained access to my Google account, so I'm hoping to gain some more information. The device cannot be found in ADM, likely because the app is not installed and set up, but I have access to the device in the web version of the Play Store, so I can install apps to it. So here's my question - are there any device location apps I can install to the phone to help me determine where this device is? I don't really want to confront anybody, but this would give me an indication of whether this could be someone I know. Is there a different method you could recommend to gain any other insight into where this mystery device came from or how it came to be associated with my account?