Вариант:  
Sub ShowAdrCells()  
Dim TxtForFind As String, RngForFind As Range, FirstAddress As String, i As Integer  
TxtForFind = "Маша"  
   For i = 1 To Sheets.Count  
       With Sheets(i).UsedRange  
           Set RngForFind = .Find(TxtForFind, LookIn:=xlValues, LookAt:=xlWhole)  
           If Not RngForFind Is Nothing Then  
               FirstAddress = RngForFind.Address  
               Do  
                   MsgBox "Искомое значение найдено в ячейке: " & RngForFind.Address(0, 0) & "  на листе: " & Sheets(i).Name, 64, "Для сведения..."  
                   Set RngForFind = .FindNext(RngForFind)  
                   Loop While RngForFind.Address <> FirstAddress  
           End If  
       End With  
   Next  
End Sub