What else can I do if a journal editor ignores my report of plagiarism?
Given your addendum, what you are talking about is not plagiarism. It might be a case of insufficient attribution, but without seeing the papers and knowing the field it is impossible to tell. 

You are guaranteed to fail in your efforts, and to make yourself look bad in the process, if you accuse this famous researcher of the wrong transgression simply because you don't know the difference between plagiarism and insufficient attribution. 

As an aside, the fact that you don't know this difference makes me question whether you are able to objectively judge whether or not the researcher in question has violated the norms of your field. I'd strongly advise seeking advice from a trusted senior mentor before doing anything.