Use curiosity and a sense of mystery to intrigue your audience and incentivise them into referring.

For example, subscribers could unlock a "mystery" video or other content when they make three referrals. Or you might ship them a "mystery" gift box when they hit 25 referrals.

In general, fewer of your subscribers will be incentivised by an unknown reward. But there'll be a few subscribers who really want to discover what the mystery reward is. And they'll be hooked.

Often, the best rewards are unique to your audience. And this is true for physical rewards too.

What's a unique, more creative physical reward you know your audience would be excited to win?

For example, if you have a local newsletter, why not try local items as rewards? (Maybe sponsored by a local business)

Or — if your newsletter is in a specific niche like the travel or sports verticals — how about a branded luggage tag or a custom sports bottle?