I know it seems like common sense, but I have never seen a fellow Priest make use of this spell:
Mind Vision
If you know the name of the player that took your flag, type it in after target. eg. a Druid named Istealflg has your flag
type in:
/tar istealflg
then cast Mind Vision
You'll see exactly where he's hiding and avoid having to waste time tracking him down. Again, I know it should be common sense, but I can't count the number of times my fellow Horde couldn't find the FC, or the number of times I successfully hid the flag for a good 10+ minutes without being found. If you're not a priest yourself, you can always ask in /bg chat for your priest to do this. It can save a lot of time, and (most times) also lets you know how many people are with the flag carrier.