David Li possesses a can-do work ethic and a willingness to zip around Beijing's harrowing traffic on an electric scooter. That makes him highly valuable to a multibillion-dollar Chinese electronic-commerce industry struggling with how to deliver goods to demanding customers.

In 2011 Mr. Li left behind a wife, infant son and a job teaching middle-school math in the eastern city of Handan to became a courier for Chinese Internet retailer Beijing Jingdong Century Trading Co., which runs the 360buy.com shopping site.

Delivery companies say couriers who work the most profitable office buildings in large cities