Former equity analyst here. Nobody on "The Street" is actually valuing these companies on PE ratios. Tech companies often intentionally re-invest earnings back into the business in real time and so their reported EPS is often quite low and a poor metric to evaluate the underlying business on. So instead, analysts typically use other metrics like EV/EBITDA or even P/Sales ratios in their valuation models.

Very generally speaking, trading these companies is kind of more of like placing a bet on whether or not their future top-line growth will be dramatically different than the market's current expectations.