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You seem to be intentionally ignoring that they don't need 290% type growth to reach FB's sales multiple rapidlyThey need at least 290% growth to reach parity with Facebook on a PRG basis. This is a mathematical fact arising from their and Facebook's numbers and the definition of the PRG ratio.
There are four components to the PEG ratio: price (P), earnings and earnings growth rate [1]. For the PRG ratio, we amend this to price, revenues (R) and revenue growth rate (G), i.e. P / (R * G * 100). We can further expand G to revenues today (R0), revenues tomorrow (R') and the years between today and tomorrow (y) using the definition of compound annual growth rate [2]. We can thus derive a fuller expression of the PRG ratio [3].
Using Facebook's FYE 2015 numbers for R0 and FYE 2016 numbers for R', where R' = R since we're using a historical R', we find a PRG ratio of 0.266 [4]. We now seek to find under what conditions Snap can make a 0.266 PRG given its current valuation. R0 = R = $404 million (FYE 2016 revenues) since we're forecasting R'. P is set by the market.
All we have to play with are R' and y related by (R' / 404 million) ^ (1 / y) = 3.833. Solving for y given R'=$2.06bn yields 1.19 years. Going from $404 million to $2.06bn in 1.19 years means a 283% growth rate.
The math is unyielding. In one year, Snap needs $1.5bn (in 2 and 3 years $5.9bn and $23bn, respectively) to hold, at a minimum, parity with Facebook based on this metric. If they don't, their PRG ratio goes up or their valuation goes down. This is a fact based on definition, not an opinion.
Valuing unprofitable high-growth companies is hard. Your quibble may be with the metric. When Snap becomes profitable it will lend itself to the far more tolerant P/E and PEG ratios. Until then, they need to grow or devalue.
[1] http://www.investopedia.com/terms/p/pegratio.asp
[2] http://www.investopedia.com/terms/c/cagr.asp
[3] PRG Ratio = P / [100 * R * ((R' / R0) ^ (1 / y) - 1)]
[4] https://news.ycombinator.com/item?id=13807118