Jess that's really tuff, If your boss is the only one that has seen his seed phrase then how did the neighbours get their hands on it, For me I think that maybe your boss saved it on his phone and while your neighbours was helping your boss out, he copied it unknown to your boss .You might have the wallet address it was sent to, but the blockchain is anonymous it won't say who or whom the money was transferred to. My Best advice is to confront the neighbour.
 If your boss had knew he would have just done some online research about how to use a wallet rather than seeking help for a neighbour and one thing about cryptocurrency once it's gone, it's gone. If it was a traditional banking system, there would have been a chance to recover it but it's not we are talking about cryptocurrency .