Citation trails link to recent articles/books which have used a specific source in their research. Found an incredibly relevant source for your topic?  Follow its citation trail to find researchers who are citing that relevant source - their research might be relevant to you as well, and even more current. 

You can often find citations of this type in library databases. For instance --

In Web of Science:

In HeinOnline:

In EconLit with Full Text:

Google Scholar is also a great source for citation trails. Just don't forget that if Google asks you to pay for an article, you should check to see if your library has that article or can get it for you for free!