I recently published a post in which I estimated the effective database sizes for Family Tree DNA, 23andMe, and MyHeritage using the published database size at AncestryDNA, which was 3 million at the time. On 22 April, 2017, AncestryDNA announced via their Twitter and Facebook feeds that their database had reached 4 million people tested. That means I underestimated the sizes of the other databases. The updated values are below.
Please see the original post for details of the analysis.