Listing wordpress users with a search function

I'm having trouble finishing off this code that I adapted from Cosmoslabs excellent tutorial. Everything is working (listing and pagination etc) except the search function whic is returning nothing i.e. no users are listed when I try to filter by a keyword.

Can anyone see what the problem might be?

Thanks for any pointers.

Osu

?php
/*
Plugin Name: WP Author Listing
Plugin URI: #
Description: Simple shortcode to list our WordPress users.
Author: OSU
Version: 1.0
Author URI: #
Licence: MIT

Many thanks for original plugin by: Cristian Antohe [http://cozmoslabs.com/]

*/

function osu_user_listing($atts, $content = null) {
    global $post;

    extract(shortcode_atts(array(
        "role" = '',
        "number" = '5'
    ), $atts));

    $role = sanitize_text_field($role);
    $number = sanitize_text_field($number);

    // We're outputting a lot of HTML, and the easiest way 
    // to do it is with output buffering from PHP.
    ob_start();

    // Get the Search Term
    // (condition) ? (true return value) : (false return value)
    $search = ( isset($_GET["as"]) ) ? sanitize_text_field($_GET["as"]) : false ;

    // Get Query Var for pagination. This already exists in WordPress
    $page = (get_query_var('paged')) ? get_query_var('paged') : 1;

    // Calculate the offset (i.e. how many users we should skip)
    $offset = ($page - 1) * $number;

    if ($search){
        // Generate the query based on search field
        $my_users = new WP_User_Query( 
            array( 
                'role' = $role, 
                'search' = '*' . $search . '*' // Assuming the problem is around here?
            ));
    } else {
        // Generate the query 
        $my_users = new WP_User_Query( 
            array( 
                'role' = '', // Default is all
                'offset' = $offset ,
                'number' = $number
            ));
    }


    // Get the total number of authors. Based on this, offset and number 
    // per page, we'll generate our pagination. 
    $total_authors = $my_users-total_users;

    // Calculate the total number of pages for the pagination
    $total_pages = intval($total_authors / $number) + 1;

    // The authors object. 
    $authors = $my_users-get_results();
?

    div class="author-search"
    h2Search authors by name/h2
        form method="get" id="sul-searchform" action="?php the_permalink() ?"
            label for="as" class="assistive-text"Search/label
            input type="text" class="field" name="as" id="sul-s" placeholder="Search Authors" /
            input type="submit" class="submit" name="submit" id="sul-searchsubmit" value="Search Authors" /
        /form
    ?php 
    if($search){ ?
        h2 Search Results for: em?php echo $search; ?/em/h2
        a href="?php the_permalink(); ?"Back To Author Listing/a
    ?php } ?

    /div!-- .author-search --

?php if (!empty($authors))  { ?
    ul class="author-list"
?php
    // loop through each author
    foreach($authors as $author){
        $author_info = get_userdata($author-ID);
        ?
        li
            ?php echo get_avatar( $author-ID, 90 ); ? 
            h2a href="?php echo get_author_posts_url($author-ID); ?"?php echo $author_info-display_name; ?/a - ?php echo count_user_posts( $author-ID ); ? posts/h2
            p?php echo $author_info-description; ?/p
            ?php $latest_post = new WP_Query( "author=$author-IDpost_count=1" ); 
            if (!empty($latest_post-post)){ ?
            pstrongLatest Article:/strong
            a href="?php echo get_permalink($latest_post-post-ID) ?"
                ?php echo get_the_title($latest_post-post-ID) ;?
            /a/p
            ?php } //endif ?
            pa href="?php echo get_author_posts_url($author-ID); ? "Read ?php echo $author_info-display_name; ? posts/a/p
        /li
        ?php
    }
?
    /ul !-- .author-list --
?php } else { ?
    h2No authors found/h2
? } //endif ?

    nav id="nav-single" style="clear:both; float:none; margin-top:20px;"
        h3 class="assistive-text"Post navigation/h3
        ?php if ($page != 1) { ?
            span class="nav-previous"a rel="prev" href="?php the_permalink() ?page/?php echo $page - 1; ?/"span class="meta-nav"lt;/span Previous/a/span
        ?php } ?

        ?php if ($page  $total_pages ) { ?
            span class="nav-next"a rel="next" href="?php the_permalink() ?page/?php echo $page + 1; ?/"Next span class="meta-nav"gt;/span/a/span
        ?php } ?
    /nav


    ?php 
    // Output the content.
    $output = ob_get_contents();
    ob_end_clean();


    // Return only if we're inside a page. This won't list anything on a post or archive page. 
    if (is_page()) return  $output;

}

// Add the shortcode to WordPress. 
add_shortcode('userlisting', 'osu_user_listing');
?