Press releases and public announcements on these aggregator websites really aren't good. You need to find some more creative way to generate publicity for your launch. Since you're working on a marketplace, what is some high-profile good or service you could offer that would draw people in? Were you to release next week, a couple hundred copies of Halo 3 might just do the trick (though at $60 a pop that could get expensive). There are too many online social sites for a simple announcement that it's up and running to draw in participants.