wp-user-query-search-by-display-name.php

<?php

function maor_twitter_run_wp_user_search_query() {
	/* There's a reason we're adding the action from here, you'll see later why. */
	add_action( 'pre_user_query', 'maor_twitter_help_main' );

	/* Create a new WP_User_Query object, limit recordset to 10 */
	$wp_user_search = new WP_User_Query(
		array(
			'number' => 10
		)
	);

	/* Make sure to remove this action since it may affect other user queries around the site. */
	remove_action( 'pre_user_query', 'maor_twitter_help_main' );

	/* Get them users! */
	$users = $wp_user_search->get_results();


	/* If $users is not null or an empty array, go on */
	if ( ! empty( $users ) ) {
		foreach ( $users as $user ) {
			printf( "My display_name is %s. My ID number is %d.", $user->display_name, $user->ID );
		}
	}
}
add_action( 'init', 'maor_twitter_run_wp_user_search_query' );

function maor_twitter_help_main( $query ) {
	global $wpdb;

	/* The display_name value you're looking to match */
	$display_name = 'Coen';

	/* Search can either be for an exact match or a partial match */
	if ( $use_like_syntax = true ) {
		$query->query_where .= $wpdb->prepare( " AND $wpdb->users.display_name LIKE %s", '%' . like_escape( $display_name ) . '%' );
	} else {
		$query->query_where .= $wpdb->prepare( " AND $wpdb->users.display_name = %s", $display_name );
	}
}