WASHINGTON - LeBron James wants you to sign up for health coverage under Obamacare. So do Magic Johnson and Jonah Hill's mom.

Monday is (sort of) the deadline for Americans without employer-provided health coverage to sign up for insurance under the Affordable Care Act - the White House extended it so that anyone who's begun to sign up by Monday can still complete the process by April 7 - and the final enrollment numbers will be an important test for a law intended to expand access for the uninsured.

It'll also be a test for the White House's high-octane sales pitch, one that's involved celebrities, YouTube videos, and paid media.

Most famously, the president himself sat down with Zach Galifianakis for an episode of his "Funny or Die" video series "Between Two Ferns." Obama promoted health-care signup and proclaimed that HealthCare.gov's glitches are a thing of the past, in a video that's been viewed on more than 3.8 million computers according to YouTube's counter.

In February, Michelle Obama appeared on "Late Night With Jimmy Fallon" to tell viewers that "now young people can get insurance for as little as $50 a month, less than the cost of gym shoes, and for the moms and dads who are out there worried about their kids, we want you to encourage your kids to sign up, for that peace of mind we all look for" - and declaring, of the infamously buggy HealthCare.gov, "It's working!"

The first lady continued her message to young people and parents in a March 14 YouTube video with some moms of famous people - Jonah Hill, Adam Levine and Jennifer Lopez.

"We nag you because we love you," Michelle Obama said at the end. "So go to HealthCare.gov and enroll today."

LeBron James also promoted signing up in a TV ad to air during NCAA-tournament basketball games:

…as did Magic Johnson:

…and Alonzo Mourning, who was diagnosed with a kidney disease during a team physical during his NBA career:

The ad blitz hasn't come cheaply. Administration officials confirmed to The New York Times that the Centers for Medicare and Medicaid Studies (CMS) will have spent $52 million on paid media to promote Obamacare enrollment from January until the end of March.

The promotional campaign has included some web ads, too, making use of the relatively new mode of "native advertising" - sponsored editorial-style content on websites.

In a "user" post on BuzzFeed, for instance, HealthCare.gov lists "7 Reasons Why Vice President Biden Thinks You Should Get Covered By March 31," in .gif form.

Illinois' health-insurance marketplace ran a sponsored post at TheOnion.com, headlined, "Onlookers Gape As Daredevil Crosses Street Without Basic Health Insurance."

The president himself, naturally, has personally promoted Obamacare enrollment over the past weeks, not just in the "Between Two Ferns" video. In an interview with Spanish-language sports-talk radio network Univision Deportes, Obama said legal residents who provide information to state exchanges or HealthCare.gov won't have to worry about immigration officials finding out about family members who are here illegally.

He recorded a video message urging Americans to sign up:

He hosted perhaps his foremost impersonator, Iman Crosson, along with other YouTube personalities at the White House this month to talk about health care:

And on Saturday, the American Association of People with Disabilities (AAPD) blasted out an email from President Obama, reading, in part:

After open enrollment ends on March 31, you won't be able to get covered through the marketplace until 2015.

Now is the time for people to get covered.

I know life is busy - and after all the troubles with the website early on, some folks have been hesitant to give it a second chance. But the website is working great now: We've signed up more than 6 million Americans already, and more are signing up every day.

It hasn't all been smooth sailing in the White House's promotional efforts.

The administration reportedly approached the National Football League about promoting Obamacare and was rebuffed, but The Washington Free Beacon reported that a White House official sent language for suggested tweets to the players' union.

"Saturday Night Live" mocked some of the gratuitous attempted social-media virality of the White House's enrollment push.

The White House has said more than 6 million people have already signed up for coverage - 1 million less than the nonpartisan Congressional Budget Office's projection of 7 million, which it lowered to 6 million after problems with HealthCare.gov.

For the president and the law, low enrollment could be a bad sign politically and for the future of the policy. For uninsured Americans, not signing up not only means not having health insurance; thanks to Obamacare's "individual mandate" and the penalty for not having insurance, it'll cost Americans either $95 or 1 percent of their household income (whichever is higher) to not have health insurance in 2014.