It may take days for the bird to become motivated enough to come down to you. Don't give up!!
While out searching listen carefully, if the bird is up in a tree or out of sight, chances are that you won't be able to see it. If the bird is vocal, you will be able to find its location by listening. It will almost always make noises that can be heard, giving direction to look in. Taking another bird out to the area may also help, especially if the other bird is a noisy friend of the lost bird or a mate or cage partner.
Call area pet stores and vets. Ask them to keep their ears open for strange telephone calls from people asking "what does a parrot eat?", "what kind of bird looks like this?" etc.
If you can't hear or locate the bird. Make and distribute flyers in the neighbourhood. Include a picture!
Notify the RSPCA. Enlist the help of neighbourhood kids. Children love to help look for lost parrots. They also tell people that are hiding them.
Don't limit your notification activity to the immediate vicinity where the bird was lost. Frightened birds often fly a long way.
Put a familiar cage and food out where it can be seen by the bird. Please ensure it's out of reach from cats and foxes.
If you have a second bird that the lost bird will recognise the calls from, put the second bird outside where the bird can hear it.
Chances are that the bird wants to get to you but are too frightened or don't know how. Often, the key is getting the bird motivated to get to you on its own. This can take a while, call calmly and soothingly to the bird.
DO NOT use a ladder or cherry picker/bucket truck or long sticks. Keep anyone and anything strange away from you that he might be afraid of. These will only frighten the bird away.
DO NOT take the popular advice to attempt to spray the bird with a hose. This too will frighten the bird, and a wet bird can still fly.
Morning and late afternoon/evening are the most likely times that the bird will come to you. It will rest in the afternoons and go to roost at night. If it is night time, do not waste your time trying to get the bird to come down. This time is better spent either resting up for the next day or working on flyers and other contacts.
If the bird is in a tree that you can climb, make sure the person climbing is someone the bird is comfortable with. Bring a favourite treat with you. If you can reach the bird, calmly secure it and stuff it under your shirt so it can't get frightened and fly away again.
If the bird has been out for a while pack a picnic and eat right under the tree where the bird is. Make sure it's something decadent and tempting such as French fries. Make a big deal about how delicious it is.
Jealousy (a Significant Other giving the bird's #1 person attention, or another rival bird or pet getting attention from said #1) can work to lure the bird down.
With time and patience, the bird will calm down and relax and become much more easily recovered. Signs of such change of state include preening, playing with leaves/branches, aborted attempts to fly down, etc.