You would want to do two things:
- Get the IP of the person posting the article
- Correlate that IP to a location
The 2nd piece is trivially easy to do, just use one of many services online (dnsstuff.com as mentioned above will work just fine).
The first piece is the more difficult one. You can ask two different people for the IP: the administrator of the site, or the hosting provider of the site. The hosting provider is only able to provide very generic logs, and is less likely to give you the information, since they tend to value their customers' privacy. So your best bet is to ask the administrator of the site for the IP address of the author. It sounds like this may not be a friendly site to you, though, so that may not be an option.
Ultimately, it depends on what you want to happen with the article. If the article is defamatory or slanderous (I'm not a lawyer) then you would probably have a decent shot at getting the hosting provider to remove the offending article.
It's easy to correlate an IP to a geographic region, but if you want to correlate this to an individual, you would need to subpoena the ISP which owns that IP range. And that's not very likely to happen.