If you want other people to spread your name around the planet, why not make it really easy for them.
You can give your advocates websites that look like they belong to them. You can give them articles and interviews that promote your cause. You can give them flyers and brochures to distribute.
The best way to really give them an incentive to promote you is if you embed an affiliate link for them in the promotional piece.It could be that a link on a web page tracks the referral from your advocate or you could give them custom printed materials or labels that has a website that only belongs to them.
Of course, you would only do this for your best advocates that have shown the ability to produce, but the little extra effort can pay off in lots of extra sales and speaking engagements.