Finding a date (dimmed as string) in entire workbook - vba

Question

I want to search all worksheets for a date, and when found replace the date by "yes".
I have the code below:
Sub Aftekenen()
Dim Sh As Worksheet
Dim Loc As Range
Dim Datum As String
Datum = "28-12-2015"
For Each Sh In ThisWorkbook.Worksheets
With Sh.UsedRange
Set Loc = .Cells.Find(What:=Datum)
If Not Loc Is Nothing Then
Do Until Loc Is Nothing
Loc.Value = "Yes"
Set Loc = .FindNext(Loc)
Loop
End If
End With
Set Loc = Nothing
Next
End Sub
However the code runs, however it never reaches the For each loop. When I remove the "-" so the date will become a number it finds it. However when the dashes are present the code does not find any fitting value, however these are present.

Answer 1

try this, for each ... next method with comparing .Text (not value, because of value of the cell for "28-12-2015" is 42366), it works well but some users have an objection to this method by some reasons, as for me less coding better reading
Sub Aftekenen()
Dim Sh As Worksheet, Loc As Range, Datum As String
Application.ScreenUpdating = 0
Datum = "28-12-2015"
For Each Sh In ThisWorkbook.Worksheets
For Each Loc In Sh.UsedRange
If Loc.Text = Datum Then Loc.Value = "Yes"
Next Loc
Next Sh
Application.ScreenUpdating = 1
End Sub
update
if you prefer .find method then for searching of the dates is required to switch Application.FindFormat.NumberFormat to format of the cells with dates, due to the date in .text is 18-05-2015, but .value is 42142
below is your updated variant
Sub Aftekenen()
Dim Sh As Worksheet
Dim Loc As Range
Dim Datum As String
Application.FindFormat.NumberFormat = "dd-mm-yyyy"
Datum = "28-12-2015"
For Each Sh In ThisWorkbook.Worksheets
With Sh.UsedRange
Set Loc = .Cells.Find(Datum, , xlValues, , , , True, , True)
If Not Loc Is Nothing Then
Do Until Loc Is Nothing
Loc.Value = "Yes"
Set Loc = .FindNext(Loc)
Loop
End If
End With
Set Loc = Nothing
Next