Before the police, go and visit in person.
Any evasion on his part, straight down the cop shop. Mention that to him, before you do, he may change his mind.

Edit. Does your company owe him any money still? should add some leverage.
( Bartleby A dead man on vacation, Thu 7 Oct 2010, 9:50, 2 replies, latest was 15 years ago)

He doesn't know where he lives.

(Aberracion Life's getting very complicated, but a lot of fun., Thu 7 Oct 2010, 9:54, Reply)

I don't have a current address for him. I have said in an email that if he doesn't return I will have to go to the rozzers but this hasn't made any difference

(lkjshaglkasjdhglkhjz lkcvl; g;aodh;owih, Thu 7 Oct 2010, 9:55, Reply)

Are there any agencies involved in the contracting?
ask them if they have a current address, don't tell them why, just say you have some important info for him.
( Bartleby A dead man on vacation, Thu 7 Oct 2010, 9:59, Reply)

No he was a direct hire. He's worked for me for nine months and there have been no problems until now.

(lkjshaglkasjdhglkhjz lkcvl; g;aodh;owih, Thu 7 Oct 2010, 10:00, Reply)