If Hedwig, a random owl could find Sirius in a top secret location, and wizards can fly on insanely fast broomsticks, then why did the Ministry, while trying to catch Sirius, not just address an owl to Sirius and follow the owl?
Or address an owl to Voldemort to find him and follow the owl.
WTF Rowling?
[Mod edit: Removing profanity]