wp-wildcard-user-search.php

<?php
/**
 * Search for users by name and return a JSON object of matches
 *
 * An example method that demonstrates how to use wildcards (*'s) when
 * looking up users. This particular example would be used to create
 * a new endpoint that would output a JSON array of returned users.
 * Something like this would be useful for JS autocomplete queries.
 */
function skw_user_autocomplete( $search_term ) {

	// Note the astrisks
	$user_query = new WP_User_Query( array(
		'search' => '*' . $search_term . '*',
	) );

	// Get the results from the query, returning the first user
  	$users = $user_query->get_results();

	$user_ids = array();
	foreach( $users as $user ) {
		$user_ids[] = array(
			'ID'           => $user->data->ID,
			'label'        => $user->data->user_login,
			'display_name' => $user->data->display_name
		);
	}

	header( 'Content-Type: application/x-json' );
	echo $json = json_encode( $user_ids );
	die;
}