Found

Castiel has spent a year looking for the boys. After the angels fell, he couldn't just teleport to them or phone them. He didn't know their phone numbers, he hadn't remembered. All he knew was that they were in Sioux Falls, South Dakota the last time he saw them and that now they would be saving people once again. Castiel had become a hunter in order to find them.

He knew he needed to find the Winchesters, but he didn't know where to start, so he looked everywhere.