it's pretty impossible to identify a user just by 1 anonymous post on a website.(without the logs). I mean sure you can compare a person's typing style...but unless they always add "jambalaya" to their posts, it'll be next to impossible to be 100% sure.
The way it works in real life, is that you find a person's email address or a long term account on a forum, and then use that info to build up a full profile about that person. The longer the person is on the web, the more personal information they've revealed in the past.
i.e. 6 months ago they might have mentioned their phone #...so you can use whitepages to see their address. Or maybe they posted a link to their site..where they didn't have privacy enabled, so you can get the full name and address using whois. Or maybe they are using the same username on all sites, so you can use google to see all the forums they've ever posted on. etc
The way it works in real life, is that you find a person's email address or a long term account on a forum, and then use that info to build up a full profile about that person. The longer the person is on the web, the more personal information they've revealed in the past.
i.e. 6 months ago they might have mentioned their phone #...so you can use whitepages to see their address. Or maybe they posted a link to their site..where they didn't have privacy enabled, so you can get the full name and address using whois. Or maybe they are using the same username on all sites, so you can use google to see all the forums they've ever posted on. etc