From what i saw online after searching, AMD says that warranty is not transferrable even if you have proof of purchase. But, some users with a second hand AMD CPU have got it RMAed with the proof of purchase that the original owner gave them.
But, in your case you dont have invoce, and only the box. Sorry but I don't think you can claim warranty without the bill. Even if you are the first owner, invoice is the first thing they will ask you.
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