Lost Cat: White with Black Tail & Ears

The wind blow our door open from the 3rd floor of our apartment and he went out at 2am, was seen on the stairs by our unit neighbor at 4am but nothing since. He’s white with a black tail and ears (one ear is white with black next to it on top of his head). He’s got a little spot on his back by his tail that’s missing fur due to being allergic to flea salvia, could be bigger and bleeding now cause if fleas get bad will pick at himself a lot. He’s very shy and scared with loud noises and people. He’s is a emotional support pet