Well, you can't just have it say "Friends", but there are a couple of things you can do.
First of all, you could BCC it to everyone so they can only see their own e-mail address.
Or you could create a while loop and loop through all the e-mail addresses, sending 1 e-mail per loop to 1 person.
While ($i = 0; $i < count($emailsarray); $i++)
{
mail($emailsarray[$i], $subject, $message, $headers);
}