SO, after being known as the teacher who had endless pencils on her desk, I decided I needed a solution (It only took me 6 months to figure this out). Here goes:
The Pencil Wall of Shame!
Ok. You're hooked. Here's how it works. EVERY time a student wants to use a pencil, they need to ask in Spanish "¿Puedo usar un lápiz?" (This is usually enough to scare them away). If they succeed to ask, I say Ok, go write your name on a sticky note and leave it on my desk. This is so I know WHO has one of my pencils. I typically have about 3-5 sticky notes on my desk throughout the class.
When it gets to be the end of class, I say "If you borrowed a pencil, please return it and turn in your sticky note!" They must return their pencil, then walk their sticky note to me and I stick it on my hand.
Here's the kicker... IF there's a name left on my desk and I notice that one of my pencils is missing, I take their name and put it on the "Pencil Wall of Shame." It's an empty wall at the front of my room right next to the calendar and lunch menu. Having their name on this wall means that they are NEVER allowed to borrow a pencil EVER again...and maybe they're subject to ridicule by their classmates :)
So far it's worked! Most students are lazy enough that they don't want to go through the entire process, and they're afraid of having their name on display for all of my classes to see. The class really get into it too and checks on one another for me..I'll hear them yelling a student's name for them to return their pencil!
I found this to be such a great solution to my disappearing pencils! No more rogue pencil thieves!!