PayPal has launched a new mobile payments service that allows users to buy goods through a two-click checkout.

The online payments company says companies that have used Mobile Express Checkout in beta reported double-digit sales growth on their mobile stores.

Starbucks is the first company to sign up for Mobile Express Checkout. The company will use the service to let its customers with the iPhone or iPod touch reload their Starbucks cards directly from its mobile app.

PayPal also has added support to preapproved, chain and split payments to its mobile services lineup. Developers can now use preapproved payments for subscription-based business models and use split and chained payments to take a cut of transactions between buyers and sellers, the company said.

PayPal also launched a new location-based feature that lets users find nearby businesses which accept PayPal. The service is initially available in beta for iPhone users in the San Francisco Bay Area.

The company is working with application publishing company Appcelerator to help its merchants create mobile commerce apps and the two companies plan to launch a joint mobile commerce offering next year. Appcelerator’s technology allows merchants to build apps on iOS, Android and BlackBerry from one Web code base.

PayPal has been in the mobile payments space for five years and has apps for iOS, Android and BlackBerry in addition to SMS and WAP-based payment services. The company’s mobile payments service is growing rapidly. PayPal expects to close out this year with more than $700 million in mobile payments, a nearly five-fold increase over the $141 million in mobile payments PayPal processed last year.