Nintendo spilled the beans on current amiibo figures in their financial results briefing this week: approximately 50 million units to date. The company reminds us that "all" characters in the 3DS/Wii U version of Smash have been released as amiibo, hinting that they're going to be doing the same with Ultimate on Switch.
As a reminder as of the third quarter of 2016 Nintendo had pushed 20.5 million amiibo units at that point, peddling 6.5 million in the following six months, bringing the early 2017 total up to 27 million. Through March 2018 they sold 10.3 million more, and in the last seven months have bumped that up to their "approximately 50 million" figure. There's still clear growth even if most of your friends stopped buying them.
The next waves are the Splatoon 2 Octolings 3-pack and three Smash Ultimate figures (Inkling, Ridley, Wolf), followed by more in the Ultimate line. As always, here's a full list of amiibo figures: past, present and future.
Financial Results Briefing [Nintendo]