FindControl() not getting value from input textbox - asp.net

Question

I am working on a website that has input boxes which are capable of being edited. The boxes are populated from an SQL call on PageLoad() and each text box is assigned with the ID "txtz" and then the ID number from the SQL row.
I want the user to be able to edit the text box, and upon clicking a html button have the values from the input boxes stored in a variable that can be used to Update the SQL data.
My issue is that when I call CType(FindControl it is having difficulties locating the instance of the object... I would be very grateful for any and all help!
Note When I alert the variable created for the input ID it matches what is displayed as the inputs ID on the browser... leaving me to think the FindControl function is the issue.
I have attached two images from my code in hopes that it may assist!
Table Creation in PageLoad
Procedure on Button Click
Sub UpdatePostDB(sender As Object, e As EventArgs)
Dim ButtonID As String = sender.ID
Dim ButtonID2 As String() = ButtonID.Split("z")
Dim placeholder As String = ButtonID(0)
Dim realID As String = ButtonID(2) & ButtonID(3) & ButtonID(4)
Dim titleinput As String = "txtz" & realID
Dim messgeinput As String = "txtz" & realID
Dim Titl As String = CType(FindControl(titleinput), HtmlInputText).Value
Dim Messge As String = Request.QueryString("txt2z" & realID)
ClientScript.RegisterStartupScript(Me.GetType, "titlealert", "alert('Title: " & titleinput & "');", True)
End Sub
cm1.CommandText = "SELECT * FROM ManagerPosts WHERE Department = '" & DeptDDL2.SelectedItem.Text & "' And DateAdded >= DATEADD(DAY,-14,GETDATE()) ORDER BY DateAdded ASC"
dr1 = cm1.ExecuteReader
If dr1.HasRows Then
While dr1.Read
Dim viewannouncement As New TableCell() With {.HorizontalAlign=HorizontalAlign.Center}
Dim viewannounce As New CheckBox With {.ID = dr1.Item("ID"), .AutoPostBack = True}
AddHandler viewannounce.CheckedChanged, AddressOf viewannounce_CheckedChanged
Dim updateCell As New TableCell()
Dim updatebutt As New Button With {.ID = "bz" & dr1.Item("ID"), .Text = "Update Post", .Height = 25%, .Width = 85%}
AddHandler updatebutt.Click, AddressOf UpdatePostDB
Dim tr As New TableRow
If dr1("Visible") = "N" Then
tr.Cells.Add(New TableCell With {.Text = "<div style='background-color:white'><input runat='server' id=txtz" & dr1.Item("ID") & " type='text' style='width:100%;' value='" & dr1("Title") & "'/><br /><input id=txt2z" & dr1.Item("ID") & " type='text' style='width:100%;' value='" & dr1("Message") & "'/></div"})
viewannouncement.Controls.Add(viewannounce)
tr.Cells.Add(viewannouncement)
ManageTable.Rows.Add(tr)
updateCell.CssClass = "buttonup"
updateCell.Controls.Add(updatebutt)
tr.Cells.Add(updateCell)
ManageTable.Rows.Add(tr)
Else
tr.Cells.Add(New TableCell With {.Text = "<div style='background-color:white'><input id=txtz" & dr1.Item("ID") & " type='text' style='background-color: #ff66ff; width:100%;' value='" & dr1("Title") & "'/><br /><input id=txt2z" & dr1.Item("ID") & " type='text' style='background-color: #ff66ff; width:100%;' value='" & dr1("Message") & "'/></div"})
If dr1.Item("ID") = viewannounce.ID Then
viewannounce.Checked = True
End If
viewannouncement.Controls.Add(viewannounce)
tr.Cells.Add(viewannouncement)
ManageTable.Rows.Add(tr)
updateCell.CssClass = "buttonup"
updateCell.Controls.Add(updatebutt)
tr.Cells.Add(updateCell)
ManageTable.Rows.Add(tr)
End If
End While
End If
**Object reference not set to an instance of an object.
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.
Exception Details: System.NullReferenceException: Object reference not set to an instance of an object.
Source Error:
Line 146: Dim messgeinput As String = "txtz" & realID
Line 147:
Line 148: Dim Titl As String = CType(FindControl(titleinput), HtmlInputText).Value
Line 149: Dim Messge As String = Request.QueryString("txt2z" & realID)
Line 150:**