Though I hate to agree with shrinks, most believe these days that one CAN get addicted to video games, at least psychologically. Basically, just like gambling, same effect, same thing going on in the brain, and just as hard to kick.
Basically, if it is having a detrimental effect on his life, health, both physical and/or mental, and if this person is someone you care about, a friend, there is sadly, very little you can do. Trust me, talking doesn't help, telling them they are ruining their life does less than help. I am a recovering addict, I know.
Pretty much the only thing you CAN do is perhaps an intervention, talk to his family, other friends, find substance abuse councilor and get advice from them. ANY aa,NA, rehab center will have a good list of people who know about this, call them. Basically, you have to treat it like a gambling addiction. If you really are concerned, the best bet is his family and a councilor, together maybe you can get him to at least think about the fact that he might have a problems.
Realistically though, if someone does have a problem like this, there is little one can do unless the person is willing to seek help.
It is a helpless feeling I know.