Search for value and exit macro if found

Good day, Gurus.

I have a macro that copies data from the active workbook to another workbook. If the data is already in the other workbook, however, I want to give a message, "This PO Number is Already in the Tracking Log", and then exit.

The value I want to search will always be found in cell M2 of the active workbook, and I really only need to search Column M of the other workbook to see if the value is found.

Here is what I have so far. The area with the extra line breaks is where I need to add the code to search and either give the message and exit or continue to run the macro:

Sub Move_PO_to_Log()
    Dim POnumber
    Dim wbTemp As Workbook
    Set POnumber = Range("M2")
    Set wbTemp = ActiveWorkbook
    ThisWorkbook.Activate
    
    'The code below will search the whole sheet for the POnumber,
    'and then give an error if it doesn't find it.  I really need
    'it to only search Column M, and give a message and exit if
    'it finds the number, or continue if it doesn't.
    Cells.Find(What:=POnumber, After:=ActiveCell, LookIn:=xlFormulas, _
        LookAt:=xlPart, SearchOrder:=xlByRows, SearchDirection:=xlNext, _
        MatchCase:=False, SearchFormat:=False).Activate
    
    
    
    'The code belwo will work fine to copy the data needed
    'if the POnumber is not found in the search.
    wbTemp.Activate
    Range("A2:T" & Cells(Rows.Count, "A").End(xlUp).Row).Select
    Selection.Copy
    ThisWorkbook.Activate
    Range("A1048576").End(xlUp).Offset(1, 0).Select
    Selection.PasteSpecial Paste:=xlPasteValues, Operation:=xlNone, SkipBlanks _
        :=False, Transpose:=False
    Application.CutCopyMode = False
    Range("U1048576").End(xlUp).Offset(1, 0).Select
    ActiveCell.FormulaR1C1 = "=TODAY()"
    Selection.Copy
    Range(ActiveCell, "U" & Cells(Rows.Count, "A").End(xlUp).Row).Select
    ActiveSheet.Paste
    Application.CutCopyMode = False
    Selection.Copy
    Selection.PasteSpecial Paste:=xlPasteValues, Operation:=xlNone, SkipBlanks _
        :=False, Transpose:=False
    Application.CutCopyMode = False
    Range("A3").Select
End Sub

Thanks in advance for any help you can offer.

Try

Sub Move_PO_to_Log()
    Dim POnumber, c
    Dim wbTemp As Workbook
    Set POnumber = Range("M2")
    Set wbTemp = ActiveWorkbook
    ThisWorkbook.Activate
    
    'The code below will search the whole sheet for the POnumber,
    'and then give an error if it doesn't find it.  I really need
    'it to only search Column M, and give a message and exit if
    'it finds the number, or continue if it doesn't.
    Set c = Columns("M").Find(What:=POnumber.value, After:=POnumber, LookAt:=xlWhole)
    If not c is nothing then
        Msgbox "This PO Number is Already in the Tracking Log"
        Exit Sub
    End If