There is no way contact Google through Webmaster Tools about ranking changes that are caused by their algorithms. The only way to contact Google is to post in their Webmaster Central Help -- crawling, indexing, and ranking forum. However, you almost never get a response from Google there. My experience has been that you get non-helpful (sometimes even antagonistic) responses from others in the community.
In your case, the drop was likely caused by the release of Google's latest payday Loans 3.0 algorithm The timing of your drop seems to correspond with when they say they launched that algorithm. That particular algorithm is targeting webspam in the historically spammy niches of PPC (porn, pills, and casino).
Another way that I figure out what went wrong on a specific date because of Google's algorithmic changes is to follow the "Google Updates and SERP Changes" threads in WebmasterWorld's Google forums. Here is the discussion around June 17th -- there isn't anything super helpful for you there though. One other person reporting a big drop on the 18th in a non-spammy niche. When I lose a lot of rankings I generally report it there and hope that other people have a similar problem so that we can collectively figure it out.
Danny Sullivan from SearchEngineLand.com sat down with Google's Matt Cutts at SMX for the keynote speech this year. At one point, Danny requests that Google notify webmasters via Webmaster Tools that their site has been effected by an algorithm with some guidance about what the problem might be and how to go about fixing it. Matt takes the feedback as a "fair criticism".