I'm looking for the thief who stole the smith's strongbox. I only know of two groups of thieves who seem different than the spawned highland rogues. One is the group near the horse in the clearing near the gates of Valeia. The only reason they stand out is because they have a "leader". They don't appear to be it. I next thought of the Jade thieves, but no dice there either. Anyone care to toss me a hint?

Head towards Nymph Lake. You're sure to run into him.

He looks like a regular Highland Rogue, but he's "named" (and he's got a lot more HP).

-Sazerac

If you really can't find him, head over to the Crypt. By the time you get the signet, both He and Jubba Choppers should be waiting for you when you come out of the Crypt.

Did you find him?

The almost foolproof method:
1. Take the quest.
2. Leave Valeia in the direction to the graveyard.
2. Kill the robbers near the horse and return to the way to the graveyard (if they are already dead, then look at the horse and return).
3. Go to the graveyard gate.
4. Return to the town gate.
5. Enter Valeia and leave it in the direction to the graveyard. Simply enter and leave - you need not do anything else.
Mon the Sculz is now going from the horse to the way to the graveyard. Go to the horse and you should meet him.
The method works with ca. 80% chance.