If a company has more than 2000 shareholders and greater than a certain asset level it will become an INVOLUNTARY SEC registrant. It will be compelled to file a registration statement and file periodic financial reports.
That, in fact, is why Google was forced to go public when it did. It'd distributed stock to more than 300 employees--the cutoff at the time was 300 shareholders--and so needed to register with the SEC. The level was raised to 2000 shareholders of record because in many cases, equity crowdfunding efforts would attract a significant number of small investors.
In reality, very few companies reach a level at which they're compelled to register with the SEC. Most, like ARYC, register voluntarily. Those companies can deregister voluntarily, too, if they want. But while they remain registered, they are obliged to file Ks and Qs with the SEC, per the Securities Exchange Act of 1934.