I should point out that Word of Mouth and referrals is what helped PayPal get 7 to 10% daily growth during the early days of Paypal.
In Elon Musk's own words "Yeah. Well, we started off first by offering people $20 if they opened an account. And $20 if they referred anyone. And then we dropped it to $10. And we dropped it to $5. As the network got bigger and bigger, the value of the network itself exceeded any sort of carrot that we could offer."
I think cryptocurrencies also should follow a similar strategy until they get enough visibility and adoption. We can't say this for Bitcoin and Ether likes. But at-least the new coins which are failing due to lack of marketing and their anonymity could try this.
Not to forget that for some time it was mandatory for traders on Ebay to offer Paypal as a payment option. Paypal wouldn't be where it's at, if a behemoth like Ebay had not thrown its weight into the scale.