The sooner you do the below, the better chance you will have of recapturing your bird; but sometimes it can take a couple days. Might work, might not - but it worked for me with a very wild (never handled) parakeet - which had been outside for 48 hours before recapture.
1. Take 2 cages (the kind that the bird is used to).
2. Put the bird's mate (or companion) into one cage. Make sure the bird has food and water.
3. The 2nd cage should (of course) have no birds inside, but do make sure that there is food and water in it, also.
4. Take a very long (LONG) length of string and tie it onto a door of the empty cage. Rig it so that you can keep the door open while the string is taut and when you release the string - the door closes.
5. Put both cages right next to each other.
6. Rig the door on the empty cage with the string and back far away (15 feet or more). (and might as well get comfortable with a chair - because it's likely to take a while)
7. Wait. You will probably have to wait for hours, and perhaps days.
8. The escaped bird - if he is still in the area - will see his companion and likely fly down to him/her; first landing on top of the cage and searching for a way in. Eventually he will climb into the open door of the empty cage. Immediately release the string so the door closes shut.
9. Find out how and why the bird escaped, so you can make absolutely sure it never happens again.
Do not give up hope. The longer the bird is out in the wild, the hungrier and thirstier he is going to get, and more likely to enter the cage with food and water - ESPECIALLY if he sees a mate (or companion bird) in the adjacent cage. BUT the longer he is out in the wild, the more likely he is to fly further and further away.
Contrary to popular belief, pet birds do not have much of a chance at surviving in the wild. His only hope is for you (or someone else) to recapture him.