Recently I deleted some categories and wanted to display related posts to the readers who are coming from various search engines to my blog, instead of page not found error for posts under those deleted categories. I was looking for plug-in which can do this work and I found exactly what I was looking for WP Greet Box.
WP Greet Box plug-in lets you show a different greeting message to your new visitors depending on their referrer URL. Greeting messages automatically get inserted into the top of your posts upon activation. There is no need to modify theme files. Ability to detect the visitor’s search keywords from major search engines and automatically display related posts under or above the greeting message.
There are almost all popular referrers like google.com, bing.com, digg.com and more installed by default, but if your favorite referrer is not on the list then you can easily create your own!
Having these targeted greeting messages will help your blog increase exposure, loyal readership, and reader interaction.