Thanks for all the help guys!
The phone has been found!
Here's what happened. I accidently put my phone in my buddy's backpack. Easy mistake since we all have the same backpacks here at school.
He was in the same building all day and didn't really move too far. Therefore, it looked like the phone had been sitting in the same spot.
I had another class with him later, and I activated the Scream button and sure enough we could hear it! Since it was buried in his backpack, it was hard to hear, but we knew it was close. After another 10 minutes we finally tracked it down found it!
He said he kept hearing a siren going off but thought it was somewhere in the building haha I probably hit the Scream button 20 times!
So, the app works, and my Evo has been found!