Read this page as a quick path: scan the headings, use the step blocks, and escalate if the expected result does not happen.
There's no single right answer, but a practical starting point is once a month through your regular communications, plus always-on passive placements (pop-up, sticky bar, portal link) that run continuously.
Customers who haven't yet referred are not ignoring you — they often just haven't had the right moment. Repeated, gentle reminders at natural touchpoints (post-purchase, invoice, renewal, support resolution) tend to perform better than one big campaign push.
A reminder email sequence works well: send an initial announcement at launch, a follow-up 2–4 weeks later for those who didn't engage, and then a quarterly check-in. The key is to make referrals a normal part of how you communicate with customers, not a one-off campaign.