To be honest I haven't ever lost my phone, but there have been times I've been unable to locate it when I want it! Yes I know there are lots of find my phone apps but they need to be installed and setup before you get separated from your phone (so go do that now)!
Well now you just need your computer and Google. Simply type find my phone into the search box (or the address box if you use Chrome) and look what happens:
Clicking on the allow button sets Google off on a hunt and after a few seconds it should respond as follows:
Simply click on one of the options to keep your device in control.
