multithreading and passing listbox data

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        ProgressBar1.Maximum = ListBox1.Items.Count
        For i As Integer = 0 To ListBox1.Items.Count - 1
            Dim t As New Threading.Thread(AddressOf dwnld)

            t.Start(ListBox1.Items(i).ToString)
        Next

    End Sub

Public Sub dwnld(ByVal url As String)
        Try
            Dim result As String = String.Empty

            Dim txt As String = ""

            Dim request As HttpWebRequest = DirectCast(WebRequest.Create(url), HttpWebRequest)

            request.Method = "GET"

            Using stream = request.GetResponse().GetResponseStream()
                Using reader = New StreamReader(stream, Encoding.UTF8)
                    result = reader.ReadToEnd()
                End Using
            End Using

            Dim doc As New HtmlAgilityPack.HtmlDocument()

            doc.Load(New StringReader(result))

            Dim root As HtmlNode = doc.DocumentNode

            For Each link As HtmlNode In root.SelectNodes("//p")
                Dim att As String = link.InnerText.Trim
                txt = txt & att & vbCrLf
            Next

            Me.settext(txt)
        Catch ex As Exception

        End Try
    End Sub