You could write your own view template for the search results, reading the page thumbnail attribute and showing it with the result.

If its a blog you are listing, use the blog thumbnail template as a basis for a new search view. Some of the blog packages already come with such a blog search template.

You could also use one of the dynamic filter/search page list variants that also has options to show attributes of each listed item.

Or my Uber List (and Magic Data) addon includes an Uber List variant of the search results template, where each search result uses a stack as a template for the result. Then use Magic Data in the stack to pull in the respective page thumbnail attributes.

This drove me nuts a couple of years ago when I was trying to do the same thing - In case you are still trying to work this one out, you need to make a custom template for your search results block - Take a look at the instructions/code here:

http://www.concrete5.org/community/forums/customizing_c5/adding-pag...