There are certain steps you have to follow to locate phone.
1: In case you were using Android, you have to "Log On" to "Android Device Manager"using this link https://www.google.com/android/find Or "Log On" to ICLOUD in case of Apple devices following this link https://support.apple.com/kb/PH212512: Every device has a unique IMEI number of 15 digits that could be found on the device box and in the device as well. It is very important in device tracking and through it your operator can track your phone and can block it.
3: If your phone is "ON" then you can easily trace it in a single click.
4: If the location is not accessable then the very 1st step is to "LOCK" your phone.
5: You can directly "ERASE" your data as well.
6: You can use "Ring Option" also if your phone is lost at home.
7: In case you have lost your phone and also you don't know the IMEI number, then goto https://myaccount.google.com/intro/dashboard?hl=en-US , in the "Devices tab" you can see how many devices you have connected using your that google account. From there you can easily track the IMEI number.