Scouring the surrounding area in a matter of minutes was something that Castiel could do better than anyone else in the camp, considering his status as an angel. If his other self hadn't have fallen, then he could have been of some assistance, but... He knew that once angel was probably hopeless in most en devours that could once be done now.
He'd picked up on both Jack and John, but when he appeared Castiel only found the former - the one that he actually knew and was fairly familiar with. Jack seemed distressed and the angel moved closer to put a hand on his shoulder, appearing behind him in the manner that would probably scare him should he be off guard.