I'm working on a project where Google currently has over 9000 indexed entries, most of which are comments on a K2 article accidentally left open to comments by the previous developer.
According to the instructions at Google Webmaster Tools, the "remove url" tool is not to be used except in urgent situations where private data has been shared and that using the "remove url" tool otherwise may hurt the site.
How then to get Google to crawl the indexed pages (which were removed months ago!) and discover that they return 404 errors?
In an article by an SEO expert, http://www.zdnet.com/blog/seo/seo-pro-tip-how-to-remove-indexed-and-cached-content-urls-and-pages-from-google/1529 there is the suggestion to tweet the old url out to your followers and ask that they re-tweet it. I guess that's intended to make Google stand up and notice.
So here's the page that got 9000 comments: http://bit.ly/rIh9CB (You'll just get a 404, but thanks for visiting!)
Thanks for your help. I'll let you know what happens.