Dynamically update GridView results based on text entered into a textbox - asp.net

Question

I would like to dynamically update the results of a GridView based on characters that are entered into a textbox. My code currently works but only fires the update when the textbox loses focus or the user tabs out of the textbox. AutoPost is set to true for the textbox. I have the code to refresh the SQLDataSource, I just want the update to happen as the user enters characters in the textbox. I imagine this will require client side action, but not sure where to start. Thank you.
MARKUP
<asp:TextBox ID="txtSearch" runat="server" AutoPostBack="True" ViewStateMode="Enabled"></asp:TextBox>
<asp:Button ID="btnSearch" runat="server" Text="Search" />
<asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="False" DataSourceID="SqlDataSource1">
<Columns>
<asp:BoundField DataField="NameFirst" HeaderText="First Name" SortExpression="NameFirst" />
<asp:BoundField DataField="NameLast" HeaderText="Last Name" SortExpression="NameLast" />
<asp:BoundField DataField="Address" HeaderText="Address" SortExpression="Address" />
<asp:BoundField DataField="City" HeaderText="City" SortExpression="City" />
<asp:BoundField DataField="State_ID" HeaderText="State" SortExpression="State_ID" />
</Columns>
</asp:GridView>
CODEBEHIND
Protected Sub txtSearch_TextChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles txtSearch.TextChanged
GridData()
End Sub
Private Sub GridData()
Dim conString As String = ConfigurationManager.ConnectionStrings("MyConnectionString").ToString()
Dim sqlcon As New SqlConnection(conString)
Dim sqlcmd As SqlCommand
Dim da As SqlDataAdapter
Dim dt As New System.Data.DataTable()
Dim query As [String]
If txtsearch.Text = "" Then
query = "SELECT [Individual_ID], [NameFirst], [NameLast], [Address], [City], [State_ID], [ZipCode], [Comment] FROM [t_Individual] ORDER BY [NameLast], [NameFirst]"
Else
query = "SELECT [Individual_ID], [NameFirst], [NameLast], [Address], [City], [State_ID], [ZipCode], [Comment] FROM [t_Individual] WHERE [NameLast] LIKE N'%" + txtSearch.Text + "%' ORDER BY [NameLast], [NameFirst]"
End If
sqlcmd = New SqlCommand(query, sqlcon)
sqlcon.Open()
da = New SqlDataAdapter(sqlcmd)
dt.Clear()
da.Fill(dt)
If dt.Rows.Count > 0 Then
GridView1.DataSourceID = ""
GridView1.DataSource = dt
GridView1.DataBind()
Else
GridView1.DataBind()
End If
sqlcon.Close()
End Sub