Owls have an affinity for magic so they can sense witches and wizards. However, they have to be trained to carry letters. Once trained, you just have to tell the owls, verbally or otherwise, the name of the witch or wizard you wish to give the letter to and he/she will do the rest.
Ignoring the fact that Voldemort was basically a bodiless wimp before the events of the Goblet of Fire, even if he sent an owl to Harry and followed it, he would be stopped immediately by either a) Hogwarts protection, b) Harry's protection that he acquired from his mother (aka "power of love", which disappeared only after the events of the Goblet of Fire) or c) the people that Dumbledore/the Order of the Phoenix assigned to look after Harry. Also for majority of the series, I'd assume Voldemort knew Harry was inside Hogwarts' protective sphere of influence for most of the year ever year, so sending an owl to him and following it during those times is basically stupid. Plus adding the fact that they had a strong connection to each other (which Voldemort abused in the events of The Order of the Phoenix), he basically had no need to use other means to locate Harry. As far as I know, witches and wizards can't track other witches and wizards that aren't in their immediate area/they don't have a connection to (which Harry and Voldemort had), so yes owls are more powerful magical trackers than Voldemort.
ffs i have 3 exams why am i answering these questions