Christ, I wish I'd responded earlier...
Call your LOCAL police, do it now. They can talk to the interpol office in NZ and they can get through to local law enforcement in Vietnam very fast, it's been done before.
I've asked an admin to see if they can get your friend's IP address, which I hope will be posted here or directly to you. Give that to the police, that can be traced to his local ISP - anyone can do that - and the local police can trace it further. His profile also gives his location. Give that to the police.
Do not assume he is dead.
In the meantime try to find any social messaging material. Might as well post links here, myself or someone else MAY be able to glean an IP address from it or contact someone who can.
I'm in Malaysia right now, so not far off your timezone. I may be able to keep my internet on for tonight, so I may be able to help you further if you want to message me.