"We wanted to make sure that today, on World AIDS Day, people were reminded of the importance of housing and health care for people with HIV and AIDS," said Paul Hebblethwaite of the Salvation Army.
At Los Angeles County-USC Medical Center, an AIDS health fair was held for the public and staff.
More than a million Americans currently live with HIV/AIDS.
Statistics show that fewer than half of all Americans have been tested for AIDS and HIV.
Mayor Antonio Villaraigosa joined the celebration as part of the push to get more Angelinos tested.
"We're committed to continuing to work to provide the education, treatment and the drugs to reduce that population even further," Villaraigosa said.
The city of Long Beach is helping to raise awareness by lighting up some of the city's most famous landmarks in red.
The Queen Mary was one of at least 10 locations in the city to glow red to draw attention to the millions around the world living with HIV/AIDS.
In Sydney, Australia, U2 frontman Bono joined the country's prime minister as the famous Sydney Opera House and Harbour Bridge were lit up with red lights.
"The message of world AIDS Day is a message of hope," said Bono. "We will soon see an end to this dreadful little virus called HIV/AIDS."