It is a horrible thing to have a pet go missing. 

It is a terrible emotional rollercoaster.

First tip is "stay calm"

So the first tip is to try your best not to become overly agitated or distressed. It doesn't help you and it doesn't help to find your animal.

Your upset can make it worse because a distressed voice or action can scare your cat further if it is not used to being outside.

Resources

Below are three PDF files with a wealth of information on finding a lost cat.  We hope it helps.