IMHO, you should just put your referral link somewhere on your social media profiles. Then, if you want referrals, simply focus on growing an audience outside of Medium too. For instance, if you grow your Twitter account from zero to 5,000 genuine followers, those are about 5,000 people who will have checked out your profile and seen the link. A few of them will click and a fraction of those will subscribe.
In other words, you get referrals by becoming popular outside of Medium, not by continuously blasting your links out wherever you can ;)