When using a theme with Theme Blvd framework 2.5+, this will adjust search results to use the post grid display.

functions.php

<?php
/**
 * Display search results in a grid.
 */
function my_the_loop_args( $args ) {

	if ( is_search() ) {

		$args['context'] = 'grid';

	}

	return $args;

}
add_filter( 'themeblvd_the_loop_args', 'my_the_loop_args' );