if he is lost, you can try the vault 22 elevator glitch (dont know if patched). it usually shows your companions on the world map though.
If he's an active companion he'll be labled on the map, so you can just go to where he is. If he isn't, open up your console and type "00096bce moveto.player" without quotes and he'll appear in front of you. If he left because you made him mad you can't get him back, he'll just refuse.