<form action="" method="post" id="form_id">
<input type="text" name="yorum" id="yorum" size="30" placeholder="Yorum yaz...">
<input type="text" name="ad" id="ad" size="30" placeholder="Adiniz..." >
<input type="hidden" name="mesajid" id="mesajid" value="<?php echo $mesajid; ?>">
 
 
</form>
<script>
  $('#gonder').click(function(){
      $.ajax({
          type:'POST', 
          url:'posgonder.php', 
          data:$("#form_id").serialize(), 
          success:
        function(ok){
             $("#gor").html(ok);
        }
      });
  })
  </script>