$find is short for .Net's findComponent() function. This is not a standard JavaScript function and is specific to Microsoft's Ajax JavaScript library. $find returns javascript object, and a javascript object normally don't have a method called show()
Try use jquery. If you don't use it yet, you should take a look at it.
If you want to find a html element by id in jQuery, you have to use a #. Like $('#elementId')
and the call show()
$('#elementId').show();