Venmo is still growing like crazy

Venmo's rapid growth isn't showing any signs of slowing down.

As mobile payments as a whole struggle to gain widespread traction, the amount of money exchanged on the Paypal-owned app doubled last quarter from the same period last year.

The app's total transaction volume reached $6.8 billion in the last three months, according to Paypal's earnings call Wednesday.

Paypal had an otherwise rosy quarter as well, reporting one of its best performances since splitting from Ebay two years ago.

Venmo is also starting to answer some nagging questions analysts have had about its future -- namely, how will it make money?

The service is free -- unless connected to a credit card rather than a bank account -- but Venmo pays a transaction fee to financial institution every time money changes hands.

In order to even out this balance sheet, the company launched a program through which merchants like food delivery services and ticket vendors could use it for sales in exchange for a fee.

Paypal chief financial officer John Rainey said during Wednesday's call that the company is expecting a steady increase in revenue from the app. Even so, he doesn't think it will be a material factor this year.

Unlike competitors like Apple Pay and Android Pay, Venmo is more commonly used for payments among friends than with businesses.

But the app is by far the most popular choice among millennials. Of the 65 percent of young people who use mobile payments at all, more than two-thirds say Venmo is their go-to, according to a survey released this week from LendEDU.