Check User Input To Prevent Run-Time Error

what I want. It relies on an input box asking the user to enter a part code, which when found creates a duplicate copy. However, if the user enters a part that doesn't exist I get a run-time error. Can anybody point me in the right direction so when a user enters an incorrect part they get a message telling them it doesn't exist.

Private Sub SortTest_Click()
Dim s As String
Dim r As Excel. Range

Range("A2").Activate
s = InputBox("Enter the number you wish to find")
If StrPtr(s) = 0 Then
MsgBox "You must enter an existing part number!"
Else
Set r = Cells.Find(What:=s, After:=ActiveCell, LookIn:=xlFormulas, _
LookAt:=xlPart, SearchOrder:=xlByRows, SearchDirection:=xlNext, _
MatchCase:=False, SearchFormat:=False)

Range(Cells(r.Row, "A"), Cells(r.Row, "AH")).Copy
Sheets("APL").Cells(r.Row, "A").Insert Shift:=xlDown


Application.CutCopyMode = False
Application.Goto Sheets("APL").Cells(r.Row, "H")
Selection.Offset(-1, -5).ClearContents
Selection.Offset(-1, 0).Select
End If

End Sub