I am panicking because I can't find my cat.

I have not seen my cat for around a couple days. He is neutered and is both an inside and outside cat. He is eight years old and I know him well. I have been going outside continuously since yesterday to call for him. He usually comes to me when I call him. Sometimes it takes a bit, but it has been all day and he has not come. I fear for the worst. I drove around the neighborhood to try and find him, but no luck. My other cat and other neighborhood cats have answered my calls. This really worries me and I feel this is not like him. I am sick to my stomach and I can't relax or sleep. I don't know what to do. It hurts to wait.

Update: Thank you all. He has not returned yet, but I have taken the advice each one of you gave me. I put out a litter box, cat food, flyers around the neighborhood, visited local shelters, called local vets, sent alerts to shelters and vets, and paid to have a cat amber alert sent to those who live around me. I have done everything I can. I am desperate because I have such a close connection with him. It has been four days since I have seen him. I will try my best to be optimistic.

/r/CatAdvice Thread