missing cat

I'm feeling very sad. My mother just moved to a new house (25 miles from her old one) & I was in charge of getting her mostly outdoor 11 year old cat adjusted to the new place. She moved from a suburb to a more urban setting. I kept the cat in 5 days but he kept getting very restless around 3 am. Last Tuesday, I thought I would just sit outside with him for a little while (at 5:30 am!) but he immediately disappeared into a large group of bushes in front of her building. I've been looking for him ever since. I've put up flyers (& someone in the neighborhood keeps taking them down & leaving them crumpled on the ground). I've hired a company to send postcard flyers within a 1 mile radius & I've checked the local shelters. I feel so guilty & sad and I don't know what else to do.