Searching for papers on a subject I'm about to start researching myself but nothing comes up. How do I know that I've searched enough? I'm about to begin my master's research, and I'm in the process of formulating my research question. Therefore, I am searching for papers about the same topic to make sure that what I am planning to do has not been done before (at least not the way I am planning to do it), but so far I cannot find such papers.

How can I make sure that I've searched enough and that I am not missing anything obvious? I have chosen characteristic keywords from my topic and ran them in Google and Google scholar. Should I perform the same search in other places, or should that suffice?
Literature search is a skill like data analysis or writing. You need to learn the basics from an expert, find a good sample and dissect it, then try it on your own. Simply entering terms into Google is not enough or won't get you very far. 

I suggest that you 


spend time with an information specialist in the library to learn about constructing answerable questions and learning the basics of searching
learn about the basic databases used in your field and the proper way to search them through your subject librarian also at the library
locate several systematic reviews in your field and dissect their methods. Pay special attention to the databases and search terms they used.
ask your supervisor and peers for advice about the databases that they've used.


I hope that you develop a new-found respect for librarians in the end. They are a godsend.

Good luck!