The White Pages site has made it easier to do nearby / neighbor searches online.
If you have an old or current address for someone, but have been unsuccessful at contacting the person you are looking for at that address, neighbors can often shed light on the situation. Neighbors will often confirm whether or not the person still lives at the given address, move out dates etc. Some neighbors are more than willing to deliver a message to the person for you. Just be sure to follow the law when talking to neighbors, especially if you are a debt collector.
To use the White Pages nearby / neighbor search simply do a reverse address lookup or people search and then click the “Find Neighbors” link below your listing to locate possible neighbors for the given listing or address.