NEW YORK - How can marketers leverage social media such as Facebook and other viral channels to engage and reengage consumers?

From primarily PC-based social media sites such as Facebook and YouTube to Twitter and mobile social networks, viral word-of-mouth spread is vital for the success of any application. The opening keynote presentation at digiday:Apps discussed how to create sustainable applications and how to decide which monetization methods are best, while considering campaign's goals.

"The barrier to getting users for applications is lower than it ever has been," said Tim O'Shaughnessy, cofounder/CEO of LivingSocial. "Acquiring users and acquiring scale is an infinitely lower hurdle than it was before because of viral channels such as social networks.

"Brands can also reengage with users to keep them via viral tactics," he said. "From a money-making standpoint, it hasn't gotten any easier -- app developers are still in the same boat as if they're building an external destination site."

When brands are deciding which platforms to target, LivingSocial recommends focusing on Facebook and the iPhone.

The iPhone controls 90-plus percent of mobile application installations, according to LivingSocial.

"Other platforms should be a secondary focus," Mr. O'Shaughnessy said. "You are building a brand, so go where the people are -- Facebook and the iPhone."

As far as monetization, advertising is tried-and-true, although still evolving in the application space. Also, interest in micropayments for virtual goods is growing rapidly.

"Especially with social applications, it's increasingly difficult to make money," Mr. O'Shaughnessy said. "Facebook is building a currency platform where it has each user's credit card ID and developers can leverage that to get consumers to pay for things within their apps.

"Somebody, either a third party or Facebook itself, will allow developers to leverage a self-serve advertising model to feature local ads," he said. "There are also many things you can do with couponing to drive consumers in store."

In addition to monetization, brands such as Coke, Target and Simon & Schuster have ran campaigns within one of LivingSocial's applications, primarily for branding purposes.

The viral aspect of social networks and the App Store helps brands get more bang for their buck as far as marketing spend.

"Developer quality on the platform itself has actually gotten much, much better, so you can now build a deep engaging experience within the platform," Mr. O'Shaughnessy said. "New viral channels come up all the time in these platforms and it's a window of opportunity creating new ways for developers and brands to interact with users."

LivingSocial has a host of applications for Facebook, including "Virtual Bookshelf," "Restaurants," "Movies," "Polls," "Deals" and -- its most well-known -- Pick Your 5.

Viral channels lead to exponential growth of LivingSocial's user base. It didn't hurt that the company launched its Facebook applications early and got in on the ground floor.

"It's possible to add millions of people a day by leveraging a new channel, in our case Facebook," Mr. O'Shaughnessy said. "That type of growth is infrequent but not impossible -- those opportunities still exist.

"Sustaining users is key," he said. "Viral channels are not just for user acquisition anymore."

LivingSocial also has an iPhone application, although the company admits that it needs to make the mobile channel more of a priority.

"Mobile is not as much as a part of our overall strategy as it should be actually," Mr. O'Shaughnessy said. "We've primarily been focusing on entrenching our user base on Facebook.

"We do have an iPhone app that is in the low six figures as far as downloads," he said. "You can walk into the bookstore and pull up all the books on your want-to-read list with our iPhone app and we can offer coupons.

"Eventually you'll be able to scan a bar code on your phone at the point of sale to redeem them, but at this point in time we're still pretty young in that space."