I had a msn friend whom i have been talking for one year and a half. He was from Australia. But suddenly he disapeared!! He is  never online, no answers to my emails. And now i sent him another emails and i got reports of ''unaccesable mailbox" "message failed".  can someone tell me what happend? how can i find his new addy I really beg u for help

Looks like his account got deleted. You could google his addy and see if it comes up with any social networking sites he uses. From there try to contact him.

if you know some information about him, you could try these websites:

http://infobel.com (links phonebooks together for you to search)
http://switchboard.com/
http://people.yahoo.com


or can try searching for his e-mail:
http://E-mailchange.com
http://meta.rrzn.uni-hannover.de
http://nedsite.nl/search/people.htm#top

Or simply use Google. You'd be surprised at how much info you can find  about some people.

As for dedicated search engines for emails (and even addresses and telephone numbers): they are mostly funded by some companies and are many times nothing more than advertising sites or sites which only include people from a certain (sponsored) service.
(eg: those last three links provided by NiteMare).

In my experience, Google works best...