Twitter, Facebook, Instagram - the trinity of social media - have changed the way public relations professionals do business.

Where once they worked mostly to get their clients in print, more PR professionals now are needed to curate a company's Web content, devise online campaigns, and develop strategies to deal with complaints and maintain corporate reputations.

"The advent and continual evolution of social media has made PR even more critical to organizations," said Kate Shields, president of Vault Communications in Plymouth Meeting.

Shields, 40, a 20-year industry veteran, said her firm of 30 staffers has seen healthy growth since the recession and expects revenues this year to increase by 40 percent from last year. She hired five people so far this year and plans to hire two more before year's end.

The conversation Shields has with her clients has changed from "Which newspaper and magazine can I appear in?" to "Which social media platform should I be on?" and "How do I make my posts on Facebook, Twitter, and Instagram more engaging and entertaining?"

In January, Vault ran a campaign for Sara Lee's 45-calorie Delightful Bread, targeted at women looking to reduce calories in their diet.

Keeping to tradition, Shields reached out to food, wellness, and lifestyle writers at major newspapers and magazines. She also contacted lifestyle bloggers and mommy bloggers and posted a contest on Facebook asking people to share their healthy-eating success stories.

Consumers could view the stories online and vote for their favorite success story. Those who shared their stories received a T-shirt in the mail and were asked to post a picture on Facebook of themselves wearing the T-shirt with the hashtag #delightfulperson.

"Reading newspapers first thing in the morning was the standard thing. Today, checking Twitter first thing in the morning is the standard thing," said Leigh Fazzina, 42, who runs the one-woman company Fazzina & Co. Communications Consulting.

Twitter is just one tool. Public relations professionals use tools called social media listening programs to monitor mentions of their clients.

Listening tools pick up any form of online communication about a company, brand, or individual across the Internet.

The information gathered is then sorted into "buckets" by the tone and sentiment of each message and whether there could be an effect.

"We analyze how much 'Klout' someone has. An average consumer with a loud voice could have more Klout than a politician or a media personality," said Fazzina, whose specialty lies in health care. Klout is an analytics software used to measure influence on social media.

Public relations practitioners will come up with messages across social media for a client to repair or maintain the company's reputation.

"If a company does not listen or communicate through social media, it may as well close its doors because it's operating with its eyes closed and ears shut," Fazzina said.

Data released in December 2014 by IBISWorld, an Australian market research organization with offices in Los Angeles and New York, show that the American PR industry generated $11.9 billion a year and is growing at a 4.2 percent annual rate since the recession. IBISWorld estimates the industry will grow at an 3.2 percent annual clip through 2019.

Two factors drive this growth. A recovering economy allowed companies to spend more on communication. And the convergence of media platforms allowed PR firms to access corporate spending previously given to marketing and advertising, IBISWorld research analyst Gavan Blau said.

"Demand for digital media content, in addition to traditional media, has created new services for PR agencies to provide," Blau said.

Public relations agencies reported the strongest growth in demand from the technology, consumer products, and health-care sectors.

Company brand reputation and consumer perception are arguably more powerful than money and finances because they may make or break cash flows, said William Cowen, assistant professor of communication at Villanova University.

"Social media drives PR support from a luxury to a necessity," said Cowen, who also runs his own PR practice, Metrospective Communications.

Reputation is becoming more recognized as an asset that has tangible value, said Hugh Braithwaite, CEO of Braithwaite Communications.

"Some research shows reputation accounts for 40 to 50 percent of a brand's net value," said Braithwaite, who has been in PR for 30 years.

With more than 60 PR firms in the Philadelphia region, is the market too crowded?

Cowen does not think so.

Shields of Vault Communications said: "If the market was oversaturated, some of us would have failed. I've really seen my competitors grow."