Using named parameters with PDO for LIKE

I am trying to search the name field in my database using LIKE. If I craft the SQL 'by hand` like this:

$query = "SELECT * \n"
        . "FROM `help_article` \n"
        . "WHERE `name` LIKE '%how%'\n"
        . "";
$sql = $db->prepare($query);
$sql->setFetchMode(PDO::FETCH_ASSOC);
$sql->execute();

Then it will return relevant results for 'how'.
However, when I turn it into a prepared statement:

$query = "SELECT * \n"
        . "FROM `help_article` \n"
        . "WHERE `name` LIKE '%:term%'\n"
        . "";
$sql->execute(array(":term" => $_GET["search"]));
$sql->setFetchMode(PDO::FETCH_ASSOC);
$sql->execute();

I am always getting zero results.

What am I doing wrong? I am using prepared statements in other places in my code and they work fine.