Lost Big Gray Cat near GAP/Sterling Place and Plaza St

My big gray cat Chaz is lost, last seen in the backyard neighborhood between Vanderbilt Ave and Butler Place between Sterling and Plaza streets. He is friendly and loves the outdoors. He is about 10 years old with long gray hair (some say he is Russian blue). He has big paws due to his large thumbs on the front paws - very distinctive characteristic.
I have seen a black and white possum in this neighborhood and I am now very worried about my cat. I last saw him on Wed. April 12. If anyone has seen him or knows where he is, please email me! There is a reward of $100 to anyone who can return him to me. Please email [email hidden] if you see him.
Thanks very much!