Starbucks' loyaltry programme has 13.2m members in the US

"Mobile payments accounted for 30 percent of transactions in U.S. stores during the company’s third quarter, which was up from 29 percent in the previous quarter and 27 percent in Q1.
Starbucks’ Rewards program grew by 11 percent from last year; there are now 13.3 million active members in the U.S. that account for 36 percent of U.S. company-operated store sales. However, membership has remained stagnant at 13.3 million since April, when Starbucks reported its Q2 earnings. That’s also when Starbucks tweaked the program to reward customers based on money they spend rather than how often they visit."

Source:  GeekWire, 2nd November 2017