Ask HN: Early startup – equity to a marketing person?

I just recently launched my startup and need a person who would be able to help me to promote it in social media, blogs and through the other channels to basically get more users to sign up. I'm currently facing the "chicken and the egg" situation where in order to get more users I need more users. So obviously I can't pay this person, what is the reasonable percentage of equity should I give out to someone who potentially can become CMO if all goes well?