How can I easily declare that a purchase agreement is cancelled. Closing date was to have have been 8/27/12. I am the seller and the buyer never performed nor is he contacting me in any way. The earnest money check bounced. Does this PA need any formal cancellation?

No, no formal form needed.

Send them a letter by certified mail, and a copy by regular mail, that they have defaulted on the contract and you have declared the contract null and void. Make sure you keep a copy of the letter.