My cat is missing

As you maybe know he's been staying at my mothers because the boy is allergic and our apartment is pretty small. And my mom also have another cat so that he'd get a friend.
Apparently he got out yesterday. He usually tries to but he's not that hard to follow and catch again because he always gets a little nervous and stops.
I don't know how it happened exactly this time. My mother says he must have slipped out sometime last night when my sister opened the door.
I don't know the story.
But he's gone and I'm super sad and super sick. damn.

I really hope he finds his way back. He could be lost somewhere outside or being in someones home. If someone tries to take him he wouldn't mind. He loves people. Anyone.