Getting values from my dynamically created TextBoxes (c#, MasterPage, asp.net 2.0)

I have a method that creates a few TextBox controls dynamically (on a postback). Sample code:
private void Method1()
{
pnl.Controls.Add(RenderTextBox());
}

private TextBox RenderTextBox()
{
TextBox tb = new TextBox()
td.ID = "txtTestTxt0";
return tb;
}

I seem unable to get the value of "txtTestTxt0".  This is how i am attempting to get the value (please note that I am using a master page):
string myval = "";

if (Master.FindControl("cpn1").FindControls("txtTestTxt0") != null)
{
TextBox tb = (TextBox)Master.FindControl("cpn1").Fi ...