PDO: Im trying to display multiple rows from while loop using json_encode

here is my problem... i am trying to return multiple rows without refreshing the page from my a PDO statement using the 'LIKE' CLAUSE, the problem is it only returns one row and not the rest...can somebody please help me? thanks in advance

Here is my html form:

<h2>Please insert the username you would like to search for</h2>

<div align="center" id="loader_div"><span id="search_result"></span></div>

<form action="send/search.php" method="post" id="search_form">
<input type="text" id="search_username" name="get_name" />
<input type="submit" name="submitsearch" />
</form>    
<div id="get_users">

</div>

My PHP is as follows:

$search = $_POST['get_name'];

$query = $db->prepare("SELECT *
                         FROM `users`
                         WHERE `users`.`username` LIKE ? LIMIT 10");

$query->bindValue(1, "%".$search."%", PDO::PARAM_STR);

try {
     $query->execute();

     $data['success'] = true;

     while($row = $query->fetch(PDO::FETCH_OBJ)) {

     $data['users'] = " ".$row->username." ";

     echo json_encode($data);   
     exit(); 
     }

} catch (PDOException $e) {
  die($e->getMessage());     
  exit();
}

And here is my jQuery to return the PHP results:

$.ajax ({
type: "POST",
url: "send/search.php",
data: $('#search_form').serialize(),
dataType: "json",
success: function(data){
        if(data.success === true)
        {
          $("#display_users").html(data.users);
        },
error: function(xhr, status, et) {

    }
});