What if your product doesn't really have any inherent network effects? How do you incentivise your paying customers to share the platform that's giving them a competitive edge (my SaaS is B2B)?
You could do an ambassador program of some kind (check out The Skimm, they have a great one). But I wouldn't expect people to eagerly spread the word about solutions. For B2B you should be investing in content marketing and SEO above all else. Other clever ideas are like what Slack did; make it friendly enough for a consumer to use, and then that consumer ends up advocating for the product to their organization.