Plagiarism of reference? I'm currently writing my master thesis. I'm a bit conflicted with what I do... Reference stealing. 

So let's say article A talk about something that was reported from X, something else from Y and Z. 
I talk about article A and I find that X, Y and Z are actually really good too so I end up referencing them too. 
Is this considered plagiarism?

Also, let's say I'm really inspired by the introduction of a paper on the subject of my thesis. Is it considered plagiarism to take the reference of an article and use them to introduce the subject in a similar fashion, e.g., this field allowed to do that? I don't copy what is said but I use (some) of the references.

Is there such thing as reference plagiarism? From a google search, it seems that references are indeed checked (% matching) but it's mostly at the discretion of publisher/not something thoroughly enforced. Tbh I feel that it'd be difficult to enforce that even if I think it's bad. Sometimes you find sources from an article that are impossible to ignore. 

I'm wondering what people do with that. Part of the research is finding an article that concern you and then you continue your search from the references so you naturally "steal" references...
Put simply, plagiarism is fraud: it happens if you present material as if you had discovered it, when, in fact, you had not.

If you cite A, then you are certainly not committing plagiarism, because you are saying, in effect, "I did not discover this: A did." But what if it is not true that A discovered it? A might just have been quoting X, Y, and Z.

If you cite a paper by A, then you are claiming to have read it. If A's paper said, in effect, "X, Y, and Z report that ...", then you have a choice. You could read the papers by X, Y, and Z, and cite them, or you could legitimately cite "A, citing X, Y and Z".

In my opinion, if you have not even seen the papers by X, Y, and Z, you cannot legitimately cite them, but you can cite A's citation of them. You have to decide whether to rely on A's summary of the work of X, Y, and Z. If it is either tangential to your work, or so well known in your field that, in a sense, everyone knows it, then you do not need to trace the theory back to its origins. For example, if you are writing about the theory of gravity, it is not essential to cite Newton, I (1666), or whatever, but if your work seeks to overturn X's theory of blah, then you have to cite X's original work - and, dare I say, actually read it.

By way of a footnote: 'self-plagiarism' is something else entirely. It is recycling but in a bad way.

A further footnote: you cannot necessarily trust other authors' summaries of earlier work. I once found it necessary to translate a paper from its original French to make sure that it did say what other authors who cited it claimed it said: it did not!