If you are looking for solution to active your android device manager, this probably can be your alternative to make the app shows up again. These steps are seems as temporary solving, but it can go permanent with some requirement. You can visit into Google product forums where it can give you many solutions that you can try from several users who have similar problem with android device manager not working. For the first tip solving, you can do factory reset setting. Off course before you reset your device, back up your important information to prevent it from losing data. If it does not work and any changes, you can clear the cache in Google play services. Here are the complete guides for solving your problem. The data that you should clear the cache are from apps includes Play store> Download manager> Google service framework> and then restart your device.
First fire up the Google Play store app. Wait your device shows up again in Play store web. If your device has shows up in Play Store with the registered date, then proceed into next step. Open Google setting> security> android device manager> uncheck allow remote factory reset. Go back to device setting menu>apps>all> Google Play services> clear data. Forward to Google setting>security> allow remote factory reset> restart the device. Always do the step by step in order and wait for the device to shows appears bin web in Google Play store before you complete to stick the order. When you skip the order part, this just wastes your time. Your device should be appears to shows again about half hour into more several hours depend to the device speed. Check to the Google update forums for any tips if your android device manager not working.