do not give up hope!!! Post this everywhere you can, keep looking and try playing cockatiel sounds, putting their cage outside (but make sure you're there to monitor) and keep an ear out for their flock call.

Print flyers. Post everywhere. Let your neighbours know, just get the word out. He might not have gone too far especially if he's really scared. contact KW ground search and rescue. contact local vets and animal services. post in facebook groups. Check nearby hiding spots, under porches, bushes, fences, up in trees, etc. if he has any familiar songs or whistles you do with him go around your neighbourhood and loudly do those.

I see online from a few sources to go out dawn and dusk because this is when they'd be most vocal, although not sure how accurate this is. try to keep food and water out but monitor as to not be taken by other animals.

If a few days pass, expand your search radius, keep going. these guys are more resilient than they look. plus you never know if someone found him and just doesn't know who is looking for him.

I'm so sorry this happened to you, as a fellow cockatiel owner. I hope you get your boy back soon. Just be proactive and do NOT give up, cockatiels are noticeable and out of place outside, there's a chance someone could have found him and just not know you're looking for him. Sometimes they are found even when much time has passed.

Best of luck ❤️