i just had this happen with a baby boa..

look EVERYWHERE. get someone who knows cars and how to take apart certain pieces. If you know where he was when he got out, start there.

I ended up finding my girl inside the passenger seat gears that control the arm rest. If my friends who knew cars weren't there i would have NEVER found her. Granted, i have a Nissan and apparently they are held together by locking plastic pins (???) but it was useful to have someone there who knew how to take the car apart and put it back together.

For future reference, always SECURE reptiles in snake bags or taped transport deli cups. I hope you find him.