FindControlsRercursive.cs

using System.Collections.Generic;
using System.Text.RegularExpressions;
using System.Web.UI;

public static class ControlHelpers
{
    public static IEnumerable<Control> FindControlsRecursive(this Control root, string regex)
    {
        foreach (Control child in root.Controls)
        {
            if (!string.IsNullOrWhiteSpace(child.ID))
            {
                if (Regex.Match(child.ID, regex).Success)
                {
                    yield return child;
                }
            }

            if (child.Controls.Count > 0)
            {
                foreach (Control c in FindControlsRecursive(child, regex))
                {
                    yield return c;
                }
            }
        }
    }
}