Hi,

Here I have created sample that full-fill your requirement.

Note: If you want to do below using stored procedure use below link to split textbox value in sql and pass it in query(i.e. SELECT * FROM tbl WHERE Name IN (SELECT * FROM dbo.SplitString(@Name))).

Split and convert Comma Separated (Delimited) String to Table in SQL Server

HTML

<div>
    Search:
    <asp:TextBox ID="txtSearch" runat="server" />
    <asp:Button Text="Search" runat="server" OnClick="Search" />
    <hr />
    <asp:GridView ID="gvCustomers" runat="server" AutoGenerateColumns="false">
        <Columns>
            <asp:BoundField HeaderStyle-Width="150px" DataField="ContactName" HeaderText="Contact Name"
                ItemStyle-CssClass="ContactName" HtmlEncode="false" />
            <asp:BoundField HeaderStyle-Width="150px" DataField="City" HeaderText="City" />
            <asp:BoundField HeaderStyle-Width="150px" DataField="Country" HeaderText="Country" />
        </Columns>
    </asp:GridView>
</div>

Code

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

protected void Search(object sender, EventArgs e)
{
    this.BindGrid();
}

private void BindGrid()
{
    string constr = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
    using (SqlConnection con = new SqlConnection(constr))
    {
        using (SqlCommand cmd = new SqlCommand())
        {

            cmd.Connection = con;
            string resultCont = string.Empty;
            if (!string.IsNullOrEmpty(txtSearch.Text))
            {
                string[] contactNames = txtSearch.Text.Trim().Split(',');

                foreach (string cont in contactNames)
                {
                    if (!string.IsNullOrEmpty(cont))
                    {
                        resultCont = resultCont + ",'" + cont + "'";
                    }
                }
                resultCont = resultCont.Remove(0, 1);
                cmd.CommandText = "SELECT ContactName, City, Country FROM Customers WHERE ContactName IN (" + resultCont + ")";
            }
            else
            {
                cmd.CommandText = "SELECT ContactName, City, Country FROM Customers";
            }
            DataTable dt = new DataTable();
            using (SqlDataAdapter sda = new SqlDataAdapter(cmd))
            {
                sda.Fill(dt);
                gvCustomers.DataSource = dt;
                gvCustomers.DataBind();
            }
        }
    }
}

Screenshot

I hope this will help you out.