Besides, what does the US stand to gain from capturing Snowden other than making an example of him? He's no immediate threat to any operations or to national security.
I don't think they want to get him because it'd dramatically limit their options and possibly set a precedent with far-reaching consequences (is he a traitor? is he a hero? what does it mean to be either? is the public ready? how well would a pardon be received? if they pardon him, who else would they have to pardon? what does it mean to leak sensitive information? what does that mean for cases of espionage?)
Why address the elephant in the room when you shouldn't have brought an elephant in the room in the first place? Just let the elephant where he is.