NORTH MIAMI  — U.S. Secretary of Health and Human Services Kathleen Sebelius joined North Miami Mayor Lucie Tondreau at Joe Celestin Center on Saturday to encourage young people to sign up for health insurance under the Affordable Care Act.

Health and Human Services announced Wednesday that 3.3 million people have signed up but only 25 percent of that number are between the ages of 18 to 34.

Dozens of organizations in Florida and around the country were participating in National Youth Enrollment Day on Saturday. Events were held in Orlando, Tampa and Jacksonville to target so-called “young invincibles.” Insurers are counting on “young invincible” to offset the costs of covering older, sicker enrollees. The Obama administration has been courting young adults through social media campaigns and celebrity endorsements.

According to Census data in 2012, 18 million 19-to-34-year-olds lacked insurance – or 27 percent of all people in that age group.

The Associated Press contributed to this report.