If the group is already positively citing your first-author works, then I would say that it's not really a cold call. You may not have met, but when you get in contact, they will have some reason to distinguish you from the constant barrage of random people who email them asking for postdocs.
I would thus recommend getting in touch by noting your shared interests directly, including the fact that you've noticed their citations of your work, and being very straight-forward about your interest: you're going on the postdoc market, you've noticed the shared interests, and want to get in touch to see if there are good opportunities---either for postdoc or otherwise. This way, it's primarily about the professional relationship, not the job application, which is what's best for you as well. If they really do like your work and have funding available, they may jump to hire you. If not, it is likely to still help build future collaborations and other opportunities.
If they are negatively citing you or if you're Nth author on the works they cite, however, then it's effectively just a cold call, and you should follow the conventions of your field there.