Start new line when Enter key pressed in Multiline TextBox (TextArea) using JavaScript and jQuery

when i hit the but for next paragraph, it doesnt work on this textbox

    <script type="text/javascript">
        $(function () {
            $("[id*=Textpost]").on("keypress", function (e) {
                if (e.which != 13) {
                    var textarea = $(this)[0];
                    textarea.oninput = function () {
                        textarea.style.height = "";
                        textarea.style.height = Math.min(textarea.scrollHeight, 582) + "px";
                    };
                }
                else {
                    document.forms[0].submit();
                    return false;
                }
            });
        });
    </script>

<div class="col-lg-12">
    <asp:TextBox ID="Textpost" runat="server" class="form-control" placeholder="Thoughts..." Style="" Rows="1" cols="20" BorderStyle="Solid" Font-Bold="False" 
        autofocus="autofocus" Wrap="True" Width="100%" BorderColor="#8CC6FF" BorderWidth="1px" TextMode="MultiLine" onkeyup="return CountCharacters();"></asp:TextBox>
</div>