Musk missing

[tamsintd]

Hi all, We got two hatchings back in April, they seem happy and are growing nicely, but on Monday I discovered the smaller one had completely vanished!
He/she often buries himself in the gravel, so upon a water change on Tuesday I took the water right down to about an inch and half, removed EVERYTHING from the tank, and ran my hands through every inch of gravel - nothing. My partner found somewhere saying they're excellent climbers, so I guess we have an escapee, where should I look? Is there somewhere they'd prefer to be - dark/damp, or whatever? Oh, and how long can the little dude go without food/water?

Thanks for any advice offered