How many PCs do you allow to detect traps in a given 10' by 10' area? Two? Four? More? It seems like since the rest of the party will need to wait a turn for the thief (who, at first level is no better at the task than any of them), the rest of the party willl want to look for traps in a given suspicious area as well.
A standard door?
A standard treasure chest?
Personally, I'd allow an awful lot of PCs to search a 10' x 10' area. The potential downside is triggering the trap. Note that doesn't happen simply because they are searching, but because they say they are doing whatever my notes say the trap's trigger is (and I roll a 1 or a 2 on d6). Also, characters other than the Thief expressly cannot find magical traps. In my own current campaign, I extended this to small mechanical traps like poison needles in handles or locks; only Thieves could find them. That really isn't necessary, though. With something that small, it's perfectly reasonable that only one character can search at a time, with each attempt taking 1 Turn. That's a lot of wandering monster rolls for a 15% chance of success each time. The players can decide for themselves whether or not that's worth it.
If I had to put numbers to it (and I am not an Autarch), I'd say 6 characters per 10 x 10 area, 2 or 3 per door, 1 or 2 per chest depending on size, and 1 per lock or handle (I wouldn't make the last two cumulative). These are per Turn. My players have only ever tried this when looking for a secret door they were sure was present, mostly because of fear of triggering a trap.
I think Bobloblah's summary works perfectly as a ruling:
Each turn, up to 6 characters may simultaneously check for traps per 10 x 10 area; 3 characters may simultaneously check for traps per door; 2 characters may simultaneously check for traps per chest; and only 1 character may check for traps per lock or handle. .