Former Glee star Naya Rivera is presumed dead after going missing on a boat trip with her four-year-old son.

Authorities are continuing to search the Southern Californian lake for Rivera, who is feared to have drowned.

Authorities say she went missing after renting a pontoon boat about 1pm Wednesday, planning to go swimming with the little boy in an area of Lake Piru.

Hours later, another boater at the northern end of the lake found Rivera’s young son asleep on the boat, alone and wearing a life vest.

The busy lake is 90 kilometres north-west of Los Angeles in the Los Padres National Forest

Tweet from @VENTURASHERIFF

On Thursday morning (local time), Ventura County Sheriff’s office updated the search for the missing actress into a recovery mission.

More than 24 hours after she was last seen, more than 80 people in helicopters, drones, and all-terrain vehicles, including divers, have been involved in the search. 

“We’re going on the belief that she did go in the water and we have not been able to locate her,” Sheriff’s Captain Eric Buschow said.

“This may well be a case of drowning.”

Rivera’s identification was found on the boat and her vehicle was found in a parking area, authorities said.

The boy was safe and healthy and is with family.

Over the years, there have been occasional drownings at the popular recreation area of the lake, which is about an hour’s drive from downtown LA.

It was shut down Thursday for the search.

Fire department helicopters hovered over the water on the search’s second day, and boats of several sizes skimmed the water, with smaller ones searching up creeks and tributaries.

Rivera’s young son is from a marriage with actor Ryan Dorsey.

The couple finalised their divorce in June 2018 after nearly four years of marriage.

She called the boy, her only child, “my greatest success, and I will never do any better than him” in her 2016 memoir Sorry Not Sorry.

The most recent tweet on Rivera’s account, from Tuesday, read “just the two of us” along with a photo of her and her son.

Tweet from @NayaRivera

Rivera was engaged to rapper Big Sean in 2013, but their relationship ended a year later.

The pair met on Twitter and collaborated musically, with the rapper appearing on Rivera’s debut single Sorry.

She married Dorsey a few months later.

Singer Demi Lovato, who played a Rivera love interest in a guest stint on Glee, posted an Instagram story that showed a candle with the text, “Please pray for @nayarivera to be found safe and sound”.

Other co-stars expressed similar sentiments on social media.

“We need all the prayers we can get to bring our Naya back home to us,” Heather Morris said on Instagram.

Rivera played Santana Lopez, a singing cheerleader in the musical-comedy Glee that aired on Fox from 2009-2015.

She appeared in 113 episodes of the series and dated co-star Mark Salling. In 2018, he killed himself at the age of 35 after pleading guilty to child pornography charges.

-AAP