<form  method="post" onsubmit="return empty_form()" action="msg_popup_pr.php?reader=<?php echo $reader;?>">
<textarea name = 'message' id="message"
 style="overflow: auto; 
 word-wrap: break-word; 
 white-space: pre-wrap; 
 white-space: -moz-pre-wrap !important;  
white-space: -o-pre-wrap; 
 white-space: -pre-wrap;" 
 name='text'
 ></textarea>
<br>
<input type='submit' value='Отправить' />
</form>

function empty_form ()
	{
	    var txt = document.getElementById('message').value;
	    if(txt == '')
	    {
	        alert('введите текст.');
        return false;
	    }    
	    return true;
	}