The late Windows Phone had an app called "Find my Phone" and the iPhone has a similar app called "Find iPhone" or "iPad", but on Android, Google chose the name "Device Manager" for an app that lets you geo-locate your lost or stolen device. You will agree it is not a descriptive name. I, as a systems administrator, thought the app was meant for systems admins to manage their pool of devices in their enterprise. Add to that that I started learning developing apps for Android last year in order to better understand how software works - I developed two apps in the mean time - "Device Manager" was confusing. That is to say that "Device Manager" was really a poor choice of name. Yesterday, Google changed that.
"Device Manager" is now "Find My Phone", a simple and meaningful name. Google also redesigned the app to adopt its Material design and added some useful data such as battery and WiFi status. This info can be very useful as you will know how much time until your battery dies and to which network it is connected to. Additionally, "Find my Phone" will display the last location of your phone, which should prove useful in your quest to recover it.
Make sure you download Find My Phone in Google Play Store.