Hi elfoq,

Check this example. Now please take its reference and correct your code.

Database

For this example I have used of Northwind database that you can download using the link given below.

Download Northwind Database

HTML

Search:
<asp:TextBox ID="txtSearch" runat="server" />
<hr />
<asp:GridView ID="gvCustomers" runat="server" AutoGenerateColumns="false">
    <Columns>
        <asp:BoundField HeaderStyle-Width="120px" DataField="CustomerId" HeaderText="CustomerID" />
        <asp:BoundField HeaderStyle-Width="150px" DataField="ContactName" HeaderText="Customer Name" />
        <asp:BoundField HeaderStyle-Width="100px" DataField="OrderId" HeaderText="OrderId" />
        <asp:BoundField HeaderStyle-Width="150px" DataField="EmployeeName" HeaderText="Employee Name" />
    </Columns>
</asp:GridView>
<script type="text/javascript" src="https://ajax.googleapis.com/ajax/libs/jquery/1.8.3/jquery.min.js"></script>
<script type="text/javascript">
    $(function () {
        GetCustomers();
    });
    $("[id*=txtSearch]").live("keyup", function () {
        GetCustomers();
    });
    function SearchTerm() {
        return jQuery.trim($("[id*=txtSearch]").val());
    };
    function GetCustomers() {
        $.ajax({
            type: "POST",
            url: "CS.aspx/GetCustomers",
            data: '{searchTerm: "' + SearchTerm() + '"}',
            contentType: "application/json; charset=utf-8",
            dataType: "json",
            success: OnSuccess,
            failure: function (response) {
                alert(response.d);
            },
            error: function (response) {
                alert(response.d);
            }
        });
    }
    var row;
    function OnSuccess(response) {
        var xmlDoc = $.parseXML(response.d);
        var xml = $(xmlDoc);
        var customers = xml.find("Customers");
        if (row == null) {
            row = $("[id*=gvCustomers] tr:last-child").clone(true);
        }
        $("[id*=gvCustomers] tr").not($("[id*=gvCustomers] tr:first-child")).remove();
        if (customers.length > 0) {
            $.each(customers, function () {
                $("td", row).eq(0).html($(this).find("CustomerId").text());
                $("td", row).eq(1).html($(this).find("ContactName").text());
                $("td", row).eq(2).html($(this).find("OrderId").text());
                $("td", row).eq(3).html($(this).find("EmployeeName").text());
                $("[id*=gvCustomers]").append(row);
                row = $("[id*=gvCustomers] tr:last-child").clone(true);
            });
        } else {
            var empty_row = row.clone(true);
            $("td:first-child", empty_row).attr("colspan", $("td", row).length);
            $("td:first-child", empty_row).attr("align", "center");
            $("td:first-child", empty_row).html("No records found for the search criteria.");
            $("td", empty_row).not($("td:first-child", empty_row)).remove();
            $("[id*=gvCustomers]").append(empty_row);
        }
    };
</script>

Namespaces

C#

using System.Configuration;
using System.Data;
using System.Data.SqlClient;
using System.Web.Services;

VB.Net

Imports System.Configuration
Imports System.Data
Imports System.Data.SqlClient
Imports System.Web.Services

Code

C#

protected void Page_Load(object sender, EventArgs e)
{
    if (!IsPostBack)
    {
        BindDummyRow();
    }
}

private void BindDummyRow()
{
    DataTable dummy = new DataTable();
    dummy.Columns.Add("CustomerId");
    dummy.Columns.Add("ContactName");
    dummy.Columns.Add("OrderId");
    dummy.Columns.Add("EmployeeName");
    dummy.Rows.Add();
    gvCustomers.DataSource = dummy;
    gvCustomers.DataBind();
}

[WebMethod]
public static string GetCustomers(string searchTerm)
{
    SqlCommand cmd = new SqlCommand();
    string sql = "SELECT TOP 10 c.CustomerId, c.ContactName, o.OrderId,";
    sql += " (e.FirstName + ' ' + e.LastName) EmployeeName";
    sql += " FROM Customers c INNER JOIN Orders o on c.CustomerId = o.CustomerId";
    sql += " INNER JOIN Employees e ON e.EmployeeId = o.EmployeeId";
    if (!string.IsNullOrEmpty(searchTerm))
    {
        sql += " WHERE c.ContactName LIKE @SearchText + '%'";
        cmd.Parameters.AddWithValue("@SearchText", searchTerm);
    }
    sql += " ORDER BY NEWID()";
    cmd.CommandText = sql;
    cmd.CommandType = CommandType.Text;
    return GetData(cmd).GetXml();
}

private static DataSet GetData(SqlCommand cmd)
{
    string strConnString = ConfigurationManager.ConnectionStrings["conString"].ConnectionString;
    using (SqlConnection con = new SqlConnection(strConnString))
    {
        using (SqlDataAdapter sda = new SqlDataAdapter())
        {
            cmd.Connection = con;
            sda.SelectCommand = cmd;
            using (DataSet ds = new DataSet())
            {
                sda.Fill(ds, "Customers");
                return ds;
            }
        }
    }
}

VB.Net

Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs) Handles Me.Load
    If Not IsPostBack Then
        BindDummyRow()
    End If
End Sub

Private Sub BindDummyRow()
    Dim dummy As DataTable = New DataTable()
    dummy.Columns.Add("CustomerId")
    dummy.Columns.Add("ContactName")
    dummy.Columns.Add("OrderId")
    dummy.Columns.Add("EmployeeName")
    dummy.Rows.Add()
    gvCustomers.DataSource = dummy
    gvCustomers.DataBind()
End Sub

<WebMethod>
Public Shared Function GetCustomers(ByVal searchTerm As String) As String
    Dim cmd As SqlCommand = New SqlCommand()
    Dim sql As String = "SELECT TOP 10 c.CustomerId, c.ContactName, o.OrderId,"
    sql += " (e.FirstName + ' ' + e.LastName) EmployeeName"
    sql += " FROM Customers c INNER JOIN Orders o on c.CustomerId = o.CustomerId"
    sql += " INNER JOIN Employees e ON e.EmployeeId = o.EmployeeId"
    If Not String.IsNullOrEmpty(searchTerm) Then
        sql += " WHERE c.ContactName LIKE @SearchText + '%'"
        cmd.Parameters.AddWithValue("@SearchText", searchTerm)
    End If
    sql += " ORDER BY NEWID()"
    cmd.CommandText = sql
    cmd.CommandType = CommandType.Text
    Return GetData(cmd).GetXml()
End Function

Private Shared Function GetData(ByVal cmd As SqlCommand) As DataSet
    Dim strConnString As String = ConfigurationManager.ConnectionStrings("conString").ConnectionString
    Using con As SqlConnection = New SqlConnection(strConnString)
        Using sda As SqlDataAdapter = New SqlDataAdapter()
            cmd.Connection = con
            sda.SelectCommand = cmd
            Using ds As DataSet = New DataSet()
                sda.Fill(ds, "Customers")
                Return ds
            End Using
        End Using
    End Using
End Function

Screenshot