A manual for writers of research papers, theses, and dissertations, 7th edition - Kate L. Turabian 2007

Weblog entries and comments
Parenthetical citations–reference list style: citing specific types of sources
Part II. Source Citation

If you cite entries or comments posted on a Weblog (or blog), include the Weblog in your reference list, following the basic pattern for Web sites. Give the URL for the main page of the site.

R: The Becker-Posner blog. http://www.becker-posner-blog.com/ (accessed March 28, 2006).

Cite individual entries and comments posted to a Weblog only in parenthetical citations. The key elements, which should be separated with commas, are the name of the author, the title of the Weblog, an indication whether the item is an entry (posted by the author of the site) or a comment (posted by someone else), and the date of the posting. If an author's name is incomplete or a pseudonym, cite it as given. In many cases, you may be able to include some or all of this information in the text.

P: (Peter Pearson, The Becker-Posner Blog, comment posted March 6, 2006)

. . . according to Gary Becker (entry posted March 6, 2006, on the Becker-Posner Blog). Comments by Peter Pearson (posted March 6) and Bill (posted March 10) responded . . .