"People are suffering out there and there is little that is being done to bring assistance to them," said Carlos Marroquin, a community organizer.
Nearly 3,000 people were killed when Hurricane Maria, a Category Four system, struck the U.S. territory. It destroyed and damaged homes and knocked out power to much of the island.
Puerto Rico's governor said tens of thousands of people are still in need of reliable electricity. Demonstrators said basic human needs are not being met.
"There are still people that don't have consistent power, consistent and safe water. I'm here to have our voices be heard," said Victoria Ortiz, with Puerto Ricans in Action.
The federal government invested billions of dollars to help clean up and rebuild Puerto Rico, but some residents said they're not getting the desperately needed funds to redo their homes and feel neglected.
"Around 60 percent of the people that applied with FEMA have been denied, which means they're pretty much left to themselves trying to repair their homes," Marroquin said.
Ortiz said Puerto Ricans are just like any other U.S. citizen in need of help.
"We pay federal taxes just like any other state and we're not getting anywhere near the federal help that we should have gotten," she said.
There are several organizations in Southern California working to make sure Puerto Rico has plenty of supplies, including clean sources of drinking water.