So let’s be generous and ignore profit. How about revenue? Snap said it generated $404 million in sales in 2016. A valuation of $34 billion is about 84 times revenue.

That’s six times as high as Facebook’s price-to-sales ratio, which is 14. It’s 14 times as high as Google’s parent, Alphabet, which trades at just over six times revenue. Amazon trades at a mere three times. Even high-flying Netflix trades at seven times.

Compared with Snap, however, those are mature companies, whose growth rates have slowed somewhat as they’ve aged. As Mr. Nathanson and his fellow research analyst Perry Gold put it in a recent note to clients: “There is something brilliant about going public after only a few years of generating any revenue at all. The sky’s the limit and history is not a guide.”

To justify a valuation of even $25 billion, “you have to make some very lofty assumptions,” Mr. Hamilton said. “They would need to grow for the next 10 years at more than 50 percent every year with a profit margin of 25 percent, which is extremely high given that they are now losing money rapidly.” He noted that very few companies had achieved such growth rates in the history of American business.

But let’s ignore revenue, too. This is social media, after all, where “daily active users” and “engagement” are the coins of the realm.

By the end of 2016, Snapchat had 158 million daily active users. By comparison, Instagram, probably the closest comparison and a formidable competitor to Snapchat, had about 30 million users when Facebook bought it in 2012 for what was then considered an eye-popping price of $1 billion.