get users search not working with array

get_users looks for an exact match for the value in search in the email address, URL, ID, username or display_name fields… it doesn’t look in the first name field.

As you can’t search the first name directly, you could instead look for people with a username or display name that starts with it by using the wildcard * in the search string, e.g.:

$args=array(
   'blog_id' => $GLOBALS['blog_id'],
   'search'  => 'mark*'   /* Note the * wildcard to match anything starting with "mark" */
);
$all_users=get_users($args);
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