Lost or Stolen Mobile Device Location
(Modern Devices 2014 2015 2016 2017 2018)
In the event of lost or stolen devices, it is best to have your device prepared ahead of time.
Below are the "native" ways to do, but I will also present two other free services afterward. Generally your device has to be powered on and have connectivity. Some services offer a last seen location.
To prepare your Android device, install "Device Manager" from the Google Play Store. Login with your Google account and approve location sharing if necessary. You may need to turn on Settings->Location Access+GPS+WiFi. If you have multiple Android devices, this app will also help locate your other devices.
In the event of a lost or stolen device, visit https://www.google.com/android/devicemanager and login with your Google account that was used to setup the device. Device Manager allows you to locate, ring, lock or erase your device. (You may have to "Setup Lock & Erase" First.)
To prepare your iPhone or iPad, go to Settings->iCloud. Login if necessary (use your Apple account) and pan down to "Find my iPhone" (or iPad) and turn it on. Also turn on "Send Last Location". You may need to turn on Settings->Privacy->Location Services also.
In the event of a lost or stolen device, visit https://www.icloud.com/#find to locate your device.
Now although the above certainly work, I personally don't want to be limited to only this.
I also recommend both Prey (https://preyproject.com/) and Lookout (https://www.lookout.com/).
Prey is a free location/anti-theft app for up to three devices including laptop computers. If lost or stolen, visit https://panel.preyproject.com/app where you can locate, lock, erase, send an alert, or sound an alarm. Prey may also be able to access the front facing camera.
Lookout is a free antivirus, backup, and device-location app with additional paid backup features. Once installed and configured, visit https://www.lookout.com/d/missingDevice to locate, lock, erase, or sound an alarm.
Plan B (https://faq.lookout.com/categories/20504137-plan-b) offered by Lookout.com may also help you locate your Android device if you have not configured any previous location services.