What were the dates of Bitcoin's previous price plummets prior to 2015? What articles were written about it?
The most notable cases were:


In 2011, the price reached a peak of $32 in June, and went down all the way to $2 in November. A decrease by a x16 factor, or 93.75%.
In 2013, the price reached a peak of $266 in April, and quickly afterwards went down to the $65 range. A 75% drop.


This can be seen graphically here and here.

As for media coverage, this list of "obituaries" is handy. Among the most infamous (at least, around people who were around that long) is wired.com's 2011 piece "The Rise and Fall of Bitcoin".