Wordpress - How to search for (partial match) display names of WordPress users?

Searching the main table

Simply use WP_User_Query with a search argument.

So if you want to search for example for a user with a keyword in his user_email or similar columns from the {$wpdb->prefix}users table, then you can do the following:

$users = new WP_User_Query( array(
    'search'         => '*'.esc_attr( $your_search_string ).'*',
    'search_columns' => array(
        'user_login',
        'user_nicename',
        'user_email',
        'user_url',
    ),
) );
$users_found = $users->get_results();

Keep in mind that * is a wildcard. So restricting for example the user_email to a single domain would give you the following search string: *@example.com.

The search string has some "magic" features: The search_columns defaults to...

• user_email if @ is present in the search arg.
• user_login and ID if the search arg is numeric
• user_url if the search string contains http:// or https://
• or ... user_login and user_nicename if a string is present.

All those defaults are only set if no search_columns argument was specified.

Searching the meta table

If you want to search by for example first_name or last_name, then you'll have to do a meta_query as they're not part of the main table:

$search_string = esc_attr( trim( get_query_var('s') ) );
$users = new WP_User_Query( array(
    'meta_query' => array(
        'relation' => 'OR',
        array(
            'key'     => 'first_name',
            'value'   => $search_string,
            'compare' => 'LIKE'
        ),
        array(
            'key'     => 'last_name',
            'value'   => $search_string,
            'compare' => 'LIKE'
        )
    )
) );
$users_found = $users->get_results();

Make sure you retrieve the right search string. Normally that would be get_query_var('s');, but it could - depending on your form name/id as well be something different that you might want to retrieve using $_GET['user_search'] for example. Make sure to properly esacpe it and remove unwanted white space from the beginning and end of the string.

Keep in mind that this is an array( array() ) as there's the relation key. If you just want to have a single key searched, it might be easier to just go with the following:

$search_string = esc_attr( trim( get_query_var('s') ) );
$users = new WP_User_Query( array(
    'meta_key'     => 'first_name',
    'meta_value'   => $search_string,
    'meta_compare' => 'LIKE',
) );
$users_found = $users->get_results();

Final query

The result might look close to the following:

$search_string = esc_attr( trim( get_query_var('s') ) );
$users = new WP_User_Query( array(
    'search'         => "*{$search_string}*",
    'search_columns' => array(
        'user_login',
        'user_nicename',
        'user_email',
        'user_url',
    ),
    'meta_query' => array(
        'relation' => 'OR',
        array(
            'key'     => 'first_name',
            'value'   => $search_string,
            'compare' => 'LIKE'
        ),
        array(
            'key'     => 'last_name',
            'value'   => $search_string,
            'compare' => 'LIKE'
        )
    )
) );
$users_found = $users->get_results();