There's not much to it; you have to be in span for 10 minutes for the red message about the yellow wizard to occur, then you just run about and look for him. The blue wizards can point you to his direction, but he'll teleport every 4:30-4:40 minutes, so you might miss him if you're unlucky.
The yellow wizards are not the same for every player (he'll appear as blue for someone else while he's yellow for you), though the yellow wizards can be synced for several players. It's also possible to sync yellow wizards by lobbying untill both have the yellow one at the same location if you're going to span for several hours, so people can help eachother out and call locations.