Existing investors also participated — a list that includes Greylock Partners, Amazon, High Peaks Ventures and Chinese social media/web portal Tencent.

Also read: Viacom to sell ads on WhoSay, TwitPic to the stars

The new funding brings WhoSay’s total venture capital investment to $19.3 million. The company was quietly founded in 2010 by the incubation arm of Hollywood talent representation powerhouse Creative Artists Agency.

WhoSay allows Hollywood celebrities like Sophia Vergara and Eva Longoria to manage their photos, videos and other collateral as it gets passed around large social media platforms like Facebook, Twitter, Tumblr, YouTube and Tencent, as well as traditional media services like Associated Press.

Corporations and institutions like collegiate athletic departments use the service, too.

The company said it’ll use the capital for continued U.S. and international expansion.

“We see the ability for WhoSay members to connect directly with fans through social media as an important trend that will positively impact traditional media careers and will ultimately allow them to participate in the value they help create for online businesses as well,” said Sam Landman, partner at Comcast Venture, in a statement.

Added said Steve Ellis, CEO for WhoSay Inc.: “Comcast Ventures is a partner with deep media experience and a great track record of success. They are a perfect complement to our existing team of incredible investors and they add a vast knowledge of the marketplace in both mainstream and digital media.”

Quietly co-founded in 2010 by leading Hollywood talent representer Creative Artist Agency, WhoSay touts about 1,000 clients, ranging from movie and TV stars like James Franco and Sofia Vergara to well-known institutions like the University of Southern California Athletic Department, allowing these entities to control the rights to their photos, videos and other collateral that have been shared through social media.

Now, not only can the publicity teams of WhoSay’s clients promote their wares without losing control of their marketing collateral, but the Viacom deal allows them to monetize those assets through ad sales.

“This relationship with one of the largest media companies in the world illustrates that there is a real marketplace for this content and the engagement it creates with fans across all media,” said Steve Ellis, CEO for WhoSay Inc., in a statement.

Under the agreement, WhoSay will also work with Viacom brands such as TV networks Comedy Central, MTV, Spike, CMT and MTV to create original content and marketing integrations connected to on-air programming, online destinations and live events.

For example, prior to the formal deal, Viacom’s country-music-focused CMT partnered with WhoSay last year to promote the cable channel’s Artist of the Year awards telecast. Seven country artists participating in the event – Jason Aldean, Lady Antebellum, Rascal Flatts, Zac Brown Band, Keith Urban, Reba McEntire and The Band Perry — were WhoSay clients, and each artist gave support for the event through social media.

Funded by Amazon Investments LLC, Greylock Partners and High Peaks Ventures, WhoSay is headquartered in New York and has offices in Los Angeles and London.