I have a missing cat so I'm quite well read up on this.
Apparently indoor cats rarely move far. In fact, it's likely it could have slipped back in unnoticed so check all the usual hiding places. It may be feeling spooked after the experience so check everywhere, under beds, in cupboards etc.
Once you've established it definitely isn't indoors thoroughly comb the garden shaking treats.
After that, if no joy, go straight round to your neighbours and anyone with adjoining gardens. Speak to as many people as you can and make them aware. Show them pictures on your phone.
Then get back home and sit quietly in the garden. Talk in a soft voice to your cat. Shake treats. Chances are your cat is very near.
Rope in family and friends to go looking if your back doesn't reappear in 24 hours.
There are all sorts of tricks - scatter hoover bag, litter, put out smelly fish etc.
Best of luck. Come home soon kitty x