Arcobjects vb.net stringbuilder

I'm newbie and have question about string builder to show the arcgis layers. (System: ArcGis 10.2, VisualStudio2012) I don't succeed to show the loaded layers in a line of the message box.

code:

Imports ESRI.ArcGIS.Geodatabase
Imports ESRI.ArcGIS.Carto
Imports ESRI.ArcGIS.ArcMapUI
Imports System.Text

Public Class LayerLoop2_Button1
  Inherits ESRI.ArcGIS.Desktop.AddIns.Button

  Public Sub New()

  End Sub

  Protected Overrides Sub OnClick()

        AccessLayerViaMxDocument(My.ArcMap.Document)
        My.ArcMap.Application.CurrentTool = Nothing
    End Sub

    Shared Sub AccessLayerViaMxDocument(ByVal pMxDocument As IMxDocument)
        Dim pMap As IMap
        Dim pMaps As IMaps = pMxDocument.Maps
        Dim i As Integer

        For i = 0 To pMaps.Count - 1 Step i + 1
            pMap = pMaps.Item(i)
            Debug.WriteLine(pMap.Name)
            MsgBox(pMap.Name)

            Dim pEnumLayer As IEnumLayer = pMap.Layers(Nothing, True)
            pEnumLayer.Reset()
            Dim pLayer As ILayer = pEnumLayer.Next()
            Dim sb As System.Text.StringBuilder = New System.Text.StringBuilder()


            While Not pLayer Is Nothing

                Debug.WriteLine(pLayer.Name)
                ' Show MessageBox with the name of the layer


                pLayer = pEnumLayer.Next()

                sb.Append(pLayer.Name)
                MsgBox(sb.ToString())

            End While

        Next


    End Sub