Call the office now and ask to speak to him. If he's never given you a landline number, Google the company and go through the switchboard. Say 'good afternoon, could you put me through to Mr (check notes) Firstname Secondname, please? I think it would be the xx department.'
See what they say.
Are his parents / siblings around? Ask if he's been in touch, you are worried about him as you don't know where he is in this cold, and he doesn't seem to have taken his warm boots etc, he's out of contact and the children are anxious.
See what they say.
He will of course be angry you're doing this, because the only thing that matters is him.
Don't bother calling his friends. They aren't yours, and will lie to cover up for him.
I might be inclined to ask the police to do a welfare check, as you're concerned about his behaviour. Give the car details and his usual haunts. If they get back and say he's alive and well - but that's all the information they can give you, you have your answers. He's left and does not want you to know his location.
Are your own family available for you to go and stay for a few days? Take essentials including passports, financial stuff, etc.
I'd leave the central heating off and take any food and drink with you, for him to come home to a chilly empty house.