Use Google Scholar
Use key words on Google Scholar to find relevant papers.
Once you've found a set of relevant articles, use them to
Check their reference lists for further works.
Check the authors, see if they have other works on
Check the conference / journal the article was
published in. See if other issues have similar
Sometimes, files become unfindable - even if you had found it
before, even if you have the full title and authors. Therefore:
once you obtain the PDF of a paper and decide its relevant, keep
the file (in such a way you can find it later).
E.g. in a tool like Mendeley or Zotero, or just using
well-structured paths and filenames on your hard disk. As long
as you keep them.
Showing a hole in literature
Showing that a question has not been considered in literature
cannot be done directly. The trick is to consider various
related topics where the subject could/should have arisen. Now
you can write about related work, and simultaneously support
your assertion that the question has not yet been discussed in