You will have to check each element in the array for each value. Something like this:

Dim Duplicate As Boolean
Dim i As Long
Dim MyValue As String
MyValue = 'This is the value currently being checked
For i = 1 to UBound(MyArray)
If MyArray(i) = MyValue Then
Duplicate = True
Exit For
End If
Next i
If Duplicate = True Then
Msgbox MyArray & " is duplicated"
End If