Over the years, a lost or stolen phone is considered to be gone forever but with ths current computer age and technology advancement, your lost or stolen phone can now be tracked and recovered with ease. Also you may permenently delete your data or even locked your phone so that no one will ever have access to them. 
Without wasting much time, let's proceed to hit the nail on the head.

Must read, How to track a lost or stolen andriod phones using Android device manager.
What is android device manager and how do you use it to remotely control and even find, lock and erase your lost phone?

What is an Android Device Manager?

Android is a mobile operating system designed by Google Corporation to power and drive smart phones.

Android device manager is an android operating system based application that that allows you to view and control the hardware within which the android is run.

Read more here https://thedecentworld.com/how-to-track-a-lost-or-stolen-andriod-phones-using-device-manager