As of July 2015, Theranos is a private company, according to PrivCo. Unlike public companies, for which shares can easily be traded over exchanges, private companies have shares that can only be purchased through direct agreements between buyers and sellers, explains Investopedia.
To invest in private companies, individuals must generally be a part of an investment group, such as an angel investor or venture capital organization, notes Investopedia. Only extremely wealthy buyers, who the U.S. Securities and Exchange Commission considers accredited investors or qualified institutional buyers, are able to make such investments.
Some Theranos investors are listed by CrunchBase, including ATA Ventures, Continental Ventures, Draper Fisher Jurvetson, Tako Ventures and The Lawrence J. Ellison Revocable Trust. Other investors include Larry Ellison and Don Lucas Sr., according to Fortune. As of the middle of 2015, the company's founder, Elizabeth Holmes, also owns more than half its stock, as Fortune reports. Holmes has alluded to more recent investors, including private equity companies, but has declined to name them.
As an alternative to prospective investors attempting to directly contact such investors to negotiate the terms of a sale, shares in private companies are sometimes available through private secondary markets, according to Investopedia. These allow shareholders of private companies to more readily exchange their investments by offering them to a broader group of interested buyers.