WASHINGTON, DC - DECEMBER 21: Jaron Bell, left, passes out literature while attempting to sign up young people for healthcare. (Bill O'Leary/The Washington Post)

It’s 3 a.m., but the parking lot at the Denny’s on Benning Road in Northeast Washington is bustling. Gaggles of single women who just left the clubs. Buddies who were out joyriding. Insomniacs.

And then there is Jayna Freeman. Juggling a pile of pamphlets and ignoring the weird looks, the perky 28-year-old is trying to engage anyone she can in a conversation about something no one’s expecting at that hour: health insurance.

She waves at a man in a navy-blue hoodie. “How are you doing, sir? Have you heard about the Affordable Care Act?”

He shakes his head but looks curious. Freeman senses an opportunity and pulls him aside to make her pitch.

The dead-of-the-night outreach effort is one of a number of unconventional campaigns launched across the country in recent weeks to reach the nation’s “young invincibles” — the healthy Americans in their 20s and 30s who are key to making the economics of the new health-care law work.

The economic success of the Affordable Care Act depends on young, healthy people to enroll. The Post's Karen Tumulty takes a look at some of the states' most controversial ads selling Obamacare. (Julie Percha/The Washington Post)

Although the deadline to attempt to enroll on HealthCare.gov for coverage starting Jan.1 was 11:59 p.m. Tuesday, the uninsured actually have until March 31 to sign up and avoid a penalty.

The media blitz by the federal government, states, insurance companies and advocacy groups is shifting into high gear. To draw as many young enrollees as possible, they are trying everything from traditional print and TV ads to wacky video contests, Facebook, Twitter and Instagram campaigns, mobile apps and celebrity endorsements.

If enough young, healthy people don’t enroll to balance out those who are older and sicker, premiums could rise, which could prompt more young people to opt out and push up costs for everyone else.

A little more than a third of those enrolling through the exchanges — about 2.7 million out of the goal of 7 million next year — need to be between ages 18 and 35, according to estimates by congressional budget analysts that the White House has embraced.

The Department of Health and Human Services has declined, so far, to provide an age breakdown for the federal exchange, which is enrolling Americans in 36 states, but early numbers from some states running their own exchange show that new enrollees are skewing older, at least for now.

In California, 21 percent of the 109,296 who signed up as of Nov. 30 were between 18 and 34, slightly less than their share of the state’s population. About 35 percent of enrollees were 55 and older. In Washington state, nearly 18 percent of the 20,144 enrollees as of Nov. 30 were between 18 and 34, while 41 percent were 55 and older. In Colorado, 18 percent of the 23,009 who have enrolled as of Dec. 14 were between 18 and 34, while 28 percent were 55 and older.

The Obama administration has said that it’s premature to draw any conclusions and that it expects a rush of young people to sign up at the last minute. That’s what happened in 2007 when Massachusetts overhauled its health-care system in a similar way.

Edgier ads get attention

Getting the attention of young people is among the most difficult tasks for marketers because Americans in their 20s and 30s tend to consume information on a wide variety of mobile and social media platforms.

Some efforts related to the health-care law have been clear disappointments — such as mobile apps that few have downloaded and ads that no one talks about.

But others have gotten a lot of positive buzz, like the $2.3 million campaign launched by the ­Oregon health exchange that features videos of local artists singing catchy songs, such as “Live Long in Oregon” by Laura Gibson, about why people should get covered. (The Oregon exchange has been plagued by technical problems, however, and has had to rely on paper applications.)

Though ads targeted at all age groups have generally been upbeat, those aimed at the young are markedly edgier, featuring sex, birth control pills, keg stands and knife accidents.

In one controversial ad, a young woman stands next to a man with his arm around her. “OMG, he’s hot!” she thinks. “Let’s hope he’s as easy to get as this birth control. My health insurance covers the pill, which means all I have to worry about is getting him between the covers.”

That ad is part of the more than 30 put together for the “Got Insurance?” campaign by the Colorado Consumer Health Initiative and Progress Now.

Since the first wave of ads went up through social media in October, they have received more than 22 million hits and the feedback has been either very positive or very negative, said Adam Fox, 28, who worked on the campaign. “You need something that is going to attract a little bit of attention and get people to look at it for a few seconds.”

Laurel White, 25, a journalism graduate student at Northwestern University, said the ads could aim higher. “I wish that whoever is behind these efforts would have a little more faith in the intelligence and real-world concerns of 20-somethings,” she said.

White says that although she will be turning 26 in a few weeks and will have to leave her mother’s plan, she does not plan to buy on the exchange because she is worried there might be “problems or bugs.” Instead, she says, she will buy insurance through her university.

Other young people said in interviews over the past week that they are still confused about the details of the law and remain on the fence about signing up.

Daniel Morales, 25, of Chicago, who was uninsured and in a bad accident in October that left him with facial injuries and a large medical bill, also said he’s interested in buying on the exchange but hasn’t gotten around to doing it.

“I have friends who say it’s a joke; I don’t want to participate in it. But it’s something I want to look into. I want to form my own opinion about it,” he said.

Interested but not buying

The Denny’s between 2 and 4 a.m. on a recent Sunday morning turned out to be a surprisingly great place to find the young and uninsured. It helps that no one’s in a hurry (because nothing else is open).

Freeman, a marketing major from Howard University, is from the neighborhood. Like many other “assisters” or “navigators” hired by health exchanges across the country — she works for DC Health Link — Freeman has a personal reason for being involved. She has a good friend who received a breast cancer diagnosis at 29. The friend is alive and well, she says, thanks to having health insurance.

Of the more than 50 people she talked to that night, a few, mostly men, weren’t thrilled with the idea of buying health-care coverage.

“If I get insurance, it just benefits others. I wouldn’t use it,” said Christian Montufar, a 23-year-old construction worker, who is uninsured.

Antonio Smith, a 23-year-old who is in transportation, says he doesn’t get sick, so he isn’t interested, even though his cousin, who has insurance through her employer, keeps saying to him, “Don’t be stupid. You need it.”

Smith said he’d rather pay the fine, which would be less than the insurance, which he says he wouldn’t use.

But others were open to finding out more. Alexander Strong, 25, said his children were covered by Medicaid, but he hasn’t been insured since he lost his job at a construction company six weeks ago. His new employer doesn’t offer insurance. He made an appointment to see Freeman the following week.

Arthur Bates, a 36-year-old chef, said he hasn’t gone to a doctor in eight years but still remembers the sting of the bill for treating his cut hand: It was in the hundreds of dollars. He also signed up to talk further with Freeman at her office.

“You kind of just don’t worry about your health and insurance until you need it, but when you do, you wish you had it,” he said.

Kari Lydersen in San Diego and Meeri Kim in Philadelphia contributed to this report.