These website properties have (hundreds of) millions of engaged users. Investors are betting on the ability of Facebook, Reddit, et al to monetize those users.

These website properties have (hundreds of) millions of engaged users. Investors are betting on the ability of Facebook, Reddit, et al to monetize those users. Facebook has demonstrated a great proficiency at doing this, mostly through targeted advertising. Reddit, so far at least, has struggled but still has potential to turn their audience into a profit center.