How to search forums using Google?

I want to search forums relevant to my site’s content to post articles promotion.
Have any software or website do this? Or how to use google do this?

Thanks in advanced
Best regards,

You can’t filter the Google results to only include forums. That being said, why do you want forums so you can post your articles?

Something like this?
http://www.google.com/search?q=sitepoint&hl=en&tbo=1&tbs=dsc:1,qdr:d&ei=-suyS4zCKIruswOR4vXNAw&sa=X&oi=tool&resnum=4&ct=tlink&ved=0CB4QpwU

I have notice on some sites that, when I post i have seen posting on other sites

You can try to search for lists with forums arranged by topics, might help you finding what you search.

@dvduval: thank u, it help for me
I found one way to do this:
keyword +“powered by vbulletin”
keyword +“powered by phpbb”
keyword +“powered by ipb”

Please suggest more…
Thanks