Without doing any research on it, from the deep dark recesses of my mind I seem to remember, that there were some libel cases not that long ago (well, within the last 10 years, say), where it was held that the Claimant could sue under the laws of the country where the libellous/defamatory information was accessible. Thus, in the case of a local newspaper, any claim would probably have to be brought under the laws of the jurisdiction where it was published- in the case of the internet, however, you could be tried almost anywhere.
Therefore, as the potentially defamed party, I would first check whether the comments are available in my home jurisdiction (legitimately- i.e. that access is not normally blocked for residents of that country), then whether they would constitute a case of defamation under (in this case) Californian law, and if so, I might consider commencing proceedings in California.
Alternatively, if I fancied a trip to Europe, I might bring proceedings in Luxembourg- if nothing else, that would simplify enforcement if I was successful.