How to track someone's iphone?

My uncle went out yesterday morning and hasn't come home yet. We have tried to call his phone (not his iphone, he was going to buy a micro sim for his iphone that day) but it says the service is unavalable… I have an iphone and I was wondering if there's a way to track his? He doesn't do this, he usually calls if he's staying at his friends house for the weekend… He owed my grandparents (who we live with) money and he didn't come home to give it to them (he's done this before but he comes home that night, he has usually spent it on slot machines). I'm worried about him. Can you please help? We aren't contacting the police because my family don't think it's necessary yet.

Added (1). I don't give a *** if he's a grown man or not! He smoked weed for 20 years when he was younger so his head is pretty messed up AND he pops headache pills like candy! I'm worried that he could of over dosed or something.

Mayb

Hes a grown *** man he doesn't have to check in and prob doesn't wanna pay

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