I have not. [As far as he is concerned, very little that has happened so far would not give them a reason to be "overreacting". It is certainly not overreacting if they have truly gone missing.]

I could help you look for him, if you need a second pair of eyes. Do you see him often, or stay with him? How long has it been since you saw him last? [If it has been more than a day then he is definitely going to go looking, whether he has to do it on his own or with company.]