It is a matter of principle. But calling those who stolen your intellectual property does nothing but aggravating your grief.
I tried to rectify a similar situation. I then realise that our people are amongst the few in the world who do not observe intellectual property. Neither would our countrymen offer even an apology, let alone doing something about it.
Litigation that leads to rectification? It will cost you a fortune to hire the service of an international lawyer. If the verdict favours you, enforcing a verdict internationally has always been problematic. So think again.
I suggest that you should name them and shame them. To help advance the interest of a portal, the Webmasters or Forum moderators may want to set up a column for the original authors to make plagarism allegations. If a publication is conscious of its image and readership, it would give the plagiarists (or itself) a pad on the back at least, I'll say.