Bibtex citation keys are in no-way unique, nor do they have to be meaningful. The sole purpose of the key is to use it as a reference link when citing the work. In latex you would do something like
foobar is a perfectly valid key. To add to the confusion, there is no unique convention on naming bibtex entries, and whether there should be one is up for discussion. Some people name their own keys, others let their citation manager do the job for them. I use Mendeley which uses a FirstAuthorSurname_Year schematic. If I have more than one paper by that same author published in that same year, Menedeley appends lower-caps letters after the main key. Zotero and Google seem to do something similar.
What this means is that reverse searching an article from the bibtex key you have in your .bib file is a hard task, which might even be impossible if the keys used follow a random/meaningless scheme. If however, the key contains some data on the publication - Author, year, publication type, etc. - you can try entering those details in your favourite publication search engine in the hope of finding the paper.