What procedures should I follow if my preprint is stolen and published in a journal? I am surprised by the fact that a journal published an article that I have had in arXiv for a few months. The date of publication is after the date that I posted on arXiv. The submission date in the journal is not mentioned.  What procedures I should follow?

Some information to clarify the situation:  


The article published in the journal is a total plagiarism. They changed only the name of the title.  
The article is published in a journal in the name of other authors.  
My article (that is in arXiv) is already accepted in another journal (but not yet online) and the date of acceptance is before the date of publication of that of the other authors.
I believe the first thing you need to do is to contact and email the editor in chief of that journal and give him/her a link to your arxiv paper. 

He/She a long with the editorial board have to retract the article (hopefully, with a big red X stating that the authors have plagiarised citing your arxiv work).