It's impossible to display all the SPAM emails using a certain filter since not all the emails come the same provider. You can either take it gradually to manually input search strings to determine what are most emails send from or you can use . to display all the email to delete it.
However, instead of Search I would also use Find because there is the possibility of using advanced filters, but going through 11.000 emails will take a very large amount of time.
I also recommend checking the tutorial from the official website: http://dogsbyte.com/blscanlitetutorial.html