Hi iammann,
Please check the below code. I have done up to this. You just need to position the tooltip div respective to the textbox.
HTML
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title></title>
    <style type="text/css">
        .Tooltip
        {
            background-color: #FFFACD;
            border: 1px solid black;
            display: block;
            padding: 2px 5px 5px 5px;
            color: red;
            font-size: 8pt;
            text-align: center;
            height: 50px;
            width: 200px;
            line-height: 4;
            position: relative;
            top: -180px;
            left: 350px;
        }
    </style>
    <script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js"></script>
    <script type="text/javascript" src="http://maxcdn.bootstrapcdn.com/bootstrap/3.3.2/js/bootstrap.min.js"></script>
    <link rel="stylesheet" href="http://maxcdn.bootstrapcdn.com/bootstrap/3.3.2/css/bootstrap.min.css" />
    <script type="text/javascript">
        $(function () {
            $('input[type=text],textarea').on("focus", function () {
                if ($(this).val() == "") {
                    $('[id*=lblErrorMessage]').html($(this)[0].placeholder + " is Required");
                    $('#dvToolTip').attr('style', 'display: block');
                }
                else {
                    $('#dvToolTip').attr('style', 'display: none');
                }
            });
            $('#btnCloseToolTip').click(function () {
                $('#dvToolTip').attr('style', 'display: none');
            });
        });
    </script>
</head>
<body>
    <form id="form1" runat="server">
    <div>
        <div class="row">
            <div class="col-md-6">
                <div class="row">
                    <div class="col-md-3">
                        Name:<span style="color: red;">*</span><br />
                        <asp:TextBox ID="txtName" CssClass="required" placeholder="Name" runat="server" BackColor="#BCF2FF" />
                    </div>
                    <div class="col-md-3">
                        Subject:<span style="color: red;">*</span><br />
                        <asp:TextBox ID="txtSubject" CssClass="required" placeholder="Subject" runat="server"
                            BackColor="#BCF2FF" />
                    </div>
                </div>
            </div>
        </div>
        <div class="row">
            <div class="col-md-6">
                <div class="row">
                    <div class="col-md-3">
                        Address:<span style="color: red;">*</span><br />
                        <asp:TextBox ID="txtAddress" CssClass="required" placeholder="Address" runat="server"
                            BackColor="#BCF2FF" />
                        <br />
                        Phone/Mob:<span style="color: red;">*</span><br />
                        <asp:TextBox ID="txtPhone" CssClass="required" placeholder="Phone" runat="server"
                            BackColor="#BCF2FF" />
                    </div>
                    <div class="col-md-3">
                        Message:<span style="color: red;">*</span><br />
                        <asp:TextBox ID="txtMessage" CssClass="required" placeholder="Message" runat="server"
                            TextMode="MultiLine" Height="60px" BackColor="#BCF2FF" />
                    </div>
                </div>
            </div>
        </div>
        <br />
        <div class="row" align="center">
            <div class="col-md-6">
                <div class="row">
                    <div class="col-md-6">
                        <asp:Button ID="btnSubmit" Text="Submit" runat="server" CssClass="btn-success" /> <asp:Button
                            ID="btnReset" Text="Reset" runat="server" CssClass="btn-default" />
                    </div>
                </div>
            </div>
        </div>
    </div>
    <br />
    <div id="dvToolTip" class="Tooltip" style="display: none;">
        <div class="row">
            <div class="col-md-12">
                <img src="alert.png" style="float: left; display: table-cell; vertical-align: middle;
                    padding-top: 10px;" />
                <asp:Label ID="lblErrorMessage" runat="server" ForeColor="Red" />
                <button id="btnCloseToolTip" type='button' class='close' style="color: Black; float: right;
                    line-height: 0.5;">
                    x</button>
            </div>
        </div>
    </div>
    </form>
</body>
</html>