So sorry to hear you lost your cockatiel! That is so hard. Is there any sound (whistle or call) your bird responds to? Or maybe a special treat, like millet or peanuts or something else she might come to? Is she finger tame? Somebody told me once about a cockatiel in their yard. They knew I had one and thought it might be mine. I went over to try to catch it. The bird was perched in a tree just above my head, but he wouldn't step down to my hand, so I reached up and grabbed him. I don't know where you put your posters, but I would suggest any local vet clinics, post office, grocery store, pet stores or any other location in your area people frequent. Best wishes...I surely hope you and your little feathered friend can be re-united. Thankfully, in the warm weather, a bird can survive for quite a while.
One more idea: did your bird escape from your home or yard? If she is in the area, she just might come down to her cage if you set it outside and kept an eye on it.
Oh. God I'm sorry to read this. I lost my cockatiel last year and never got her back I'm praying you have better luck then me, it's a horrid feeling knowing your fluffy baby is out there.