1) offer a stipend. It's going to be modest, but you're a startup, so "We'll pay for your lunch, and give you enough money to rent a place with roommates," is enough.
2) Instead of ownership of revenue, give people ownership in the properties they create. Getting 10% of something questionable is okay, but being in charge of whatever new, successful lines of business you create is great.
3) Drop the '12 months' line. Tell people that you're looking for folks who can create good sites, and that if they can do it in a few months, you'll bring them on board full-time. A cut of revenue might be the right way to do things, but it makes you sound like an affiliate marketer masquerading as an internship, rather than an internship with a novel compensation scheme.