San Francisco-based video visit app Doctor On Demand raised $21 million in a round led by Venrock with additional funding from Shasta Ventures and Sir Richard Branson, the founder of Virgin Group, which offers employee wellness program Virgin Pulse.

This brings the company's total funding to $24 million.

Existing Doctor on Demand investors include Venrock, Andreessen Horowitz, Google Ventures, Lerer Ventures, Shasta Ventures and athenahealth CEO Jonathan Bush.

Doctor on Demand is currently in Rock Health's accelerator program.

Patients can use the service, available via iOS and Android apps, to connect with physicians. The company just added a web version of the service so patients can use their computers to reach doctors.

To use the service, patients request to see a doctor and are matched with one that is licensed in their state. Based on their video visit conversation, physicians can prescribe medications to patients if needed or provide the patient with another course of action. Each video call, which costs $40, can be paid for with a credit card, a health care spending account, or flexible spending account. Doctor On Demand now offers it service to 46 states, up from 15 states six months ago.

The company also announced that is has added cable company Comcast to its list of customers. Through this deal, Comcast will offer Doctor On Demand to all of its US employees and will fully subsidize the service for some employees.

“We hear every day from patients, health networks, and companies like Comcast that they want easier, faster, and more cost-effective access to high-quality healthcare,” Doctor On Demand Cofounder and CEO Adam Jackson said in a statement. “More than 85 percent of emergency room visits involve conditions that can easily be handled through video such as colds, flus, UTIs, and upper respiratory infections."

Jackson explained that when employers offer the service, they only pay when employees use it, which eliminates per-employee, per-month fees.

Besides Jackson, Doctor on Demand’s high profile team of cofounders includes former White House fellow Dr. Pat Basu and Emmy Award-winning executive producer of The Doctors Jay McGraw, whose dad is TV’s Dr. Phil. Former senate majority leader Tom Daschle and athenahealth’s CEO Jonathan Bush also serve on the company’s board.