Escapes suck I have always known them to go to lower, tight places. One of mine escaped into our basement via a heating duct. I would be sure that there's no ductwork for the snake to get into, and go from there. Pretty unlikely in my book that the snake would be up on a high shelf. Your closet sounds like a great candidate for the snake being inside.. I always did a systematic search of my apartment when snakes would escape for me in the past. That was what led me to find one snake expired in my basement (it was winter; very devastating to me) and one coiled up, very much alive, inside the underpart of our living-room sofa.

I hope that you find your snake in unharmed condition.