<?php

function limit_search_author( $query ) {

    if ( $query->is_search ) {

        $current_user = wp_get_current_user();

        if ( !( $current_user instanceof WP_User ) )
            return $query;

        if ( 0 != $current_user->ID ) {
            $query->set( 'author', $current_user->ID );
        }

    }

    return $query;

}

add_filter( 'pre_get_posts', 'limit_search_author' );

?>