Essentia
Jax Chinchilla Rescue
From the sounds of her email, the chin might not even be outside. I think I'd be looking all over for him inside as well. It seems pretty unlikely to me that a chin would go down a bunch of stairs without being noticed by the owner unless the chin wasn't being watched at all.
I explained all that to her as well. I initially thought the chinchilla was inside. She emailed me back and told me her son found droppings going down the stairs outside.