Highlighting All the Cells of Active sheet which contains a particular String:

[littleiitin]

If You want to find any string in whole sheet then Give a try to Below Code:

Sub SelectXCells(strSearch As String)

    Dim rngWhole     As Range
    Dim rngUni      As Range
    Dim lngRow      As Long
    Dim lngCol      As Long
    Dim rngCell     As Range
    
    Set rngWhole = ActiveSheet.UsedRange
    For Each rngCell In rngWhole
        If InStr(1, rngCell, strSearch, vbTextCompare) > 0 Then
            If rngUni Is Nothing Then
                Set rngUni = rngCell
            Else
                Set rngUni = Union(rngUni, rngCell)
            End If
        End If
    Next rngCell
    On Error Resume Next
    rngUni.Select
    On Error GoTo 0
End Sub

Example:

Sub Test()

    Dim strFind As String
    
    strFind = InputBox("Please enter string to find", "Find String in Used Range")
    SelectXCells (strFind)
End Sub