How I Can Get Postdata On Facebook Groupwall

Dim getUrl As String = "https://www.facebook.com/groups/1384958178382578/"
      Dim postData As String = [String].Format("xhpc_message_text={0}&_42ft _4jy0 _11b _4jy3 _4jy1 selected={1}", "eheem", "Clicked")
      Dim getRequest As HttpWebRequest = DirectCast(WebRequest.Create(getUrl), HttpWebRequest)
      getRequest.CookieContainer = New CookieContainer()
      getRequest.CookieContainer.Add(cookies)
      'recover cookies First request
      getRequest.Method = WebRequestMethods.Http.Post
      getRequest.UserAgent = "Mozilla/5.0 (Windows NT 6.1) AppleWebKit/535.2 (KHTML, like Gecko) Chrome/15.0.874.121 Safari/535.2"
      getRequest.AllowWriteStreamBuffering = True
      getRequest.ProtocolVersion = HttpVersion.Version11
      getRequest.AllowAutoRedirect = True
      getRequest.ContentType = "application/x-www-form-urlencoded"

      Dim byteArray As Byte() = Encoding.ASCII.GetBytes(postData)
      getRequest.ContentLength = byteArray.Length
      Dim newStream As Stream = getRequest.GetRequestStream()
      'open connection
      newStream.Write(byteArray, 0, byteArray.Length)
      ' Send the data.
      newStream.Close()

      Dim getResponse As HttpWebResponse = DirectCast(getRequest.GetResponse(), HttpWebResponse)
      Dim sourceCode As String
      Using sr As New StreamReader(getResponse.GetResponseStream())
          sourceCode = sr.ReadToEnd()

      End Using