You should really learn where to spam. Even if anyone wanted to use your proxy from here, they would only rape it, use your bandwidth and not click on ads.

Now to answer your promo question. Facebook and Myspace are no good for promoting proxies. Just about all of your ad clicking traffic want to go to these destinations since they are blocked.

Yahoo answers and email newsletters are the best way to promote.
Getting listed in google is the kiss of death.