Maybe a more interesting research subject would be the comparison of the American Greek system vs. the European equivalent, but that would be a study of culture and more about the superficial qualities.

There is no general way to research the American Greek system without knowing more about the core of it, the rituals, the traditions. And as an outsider, you have no way of knowing those. Also, it's hard to research something that cannot be generalized, no fraternity or sorority is the same, similar, but never the same. Even different chapters of the same (inter)national can differ greatly. How can you propose your thesis on such a subject, that cannot be measured or generalized?
As a psychology major writing my Master thesis as we speak, I think you need to define the direction of your reseach more before asking for participans.

May I ask how you came about using the topic of fraternities and sororities?

You said that you are studying "English language, literature and civilizations". Are you talking about literature written in the English language by English/British/Irish/American authors, much like what the a degree in "English" would be in the United States? For a lower-level Bachelor's degree in the US, we study literature from the middle ages to modern society in both Great Britain and the United States, which also includes talking about different class/caste systems, how peoples' lifestyles affected their writing, the religious and political climates of each era, often looking at art and music as part of the "artistic experience", etc. We also spend time learning about the language from a linguistics and etymological standpoint (the development of the English language).

Is what I wrote above, the equivalent of your study program, only on a higher ("Masters") level ?

If so, I am confused by the term "English civilizations" as part of a "Degree in English". Do you mean English-speaking societies? Are you purposefully excluding Great Britain, Ireland, Canada (mostly English speakers), and only focusing on a very small subsection of the collegiate experience in the United States?

What you are proposing is more of a sociological study on a single facet of a very small population segment of young adults in the United States. It is in not typical of the average American's experience. It's a very small number compared to the rest of "American society". Add to that the relatively secret nature of these organizations, the fact that what IS known to most of the outside world is grossly exaggerated in the media and entertainment, and that you probably aren't going to get any statistically relevant group to give you any information that you can really use.

Questions for you to answer:

1. Is this a literature study or a sociological study?

2. What is your argument/opinion/thesis statement that you hope to prove in your paper?

I am not trying to steer you away from your interest, but perhaps a comparison between something that exists in both France and the US might be a better topic for your paper.