I know this is old, but netherless...
Maby (depens on your neigbors) Inform them that there is a snake missing.
My Marhmallow found a way out of his box - I found him right under the cupbord his box stand on top. At first I thougt I had just forgotten to close the Lid. A week later he was gone (he was strong enough to open the Lid on his own). I searched the House, The rodentroom, I even rearanged almost all my furniture in hope to find him.
I never found him and thought my Cat got him (she allready had hunted wild snakes in the past).
This was just before Christmas 2014. 8 Months later in Juli 2015 my Neighbor was hysterical (I am known for all my pets and got a lot of wild animals to nurse and set wild again) there was a weird snake in her garden! I got there AND it was my Marshmallow well fed, without a scratch
Seems like he lived inside my walls since all the scratching mouse-noises were gone for the last year
So dont give up and mybe ask the neighbors