What we do for new SaaS offerings is put up a coming soon page. From here we build a buzz on a blog, new social media sites for that product, cross promote from the parent company on social and blogging... Then we invite our lists to sign up for exclusive beta spots on the coming soon page. On that page there is also social promotion to share with a friend. Be sure to find a good marketing automation platform to begin dripping these people emails, tracking all their activity and delivering information based on their interaction with your digital assets.

Beyond this I would need to know more about the platform to "fill in" the custom elements. But if you have a good creation story you can play off of that to gather some media interest ahead of time so that once you flip the switch journalists can star buzzing about you.