Authorities had been searching the lake since 8 July, when Rivera was reported missing after she rented a pontoon boat with her four-year-old son.
Monteith died from an overdose on 13 July 2013. Michele posted two black-and-white photos of both Rivera and Monteith on Instagram Stories.
Days ago, Michele – who played Rachel Berry in the hit Fox series – deleted her Twitter account after being trolled for failing to post about Rivera’s disappearance.
In the wake of the news, Michele’s co-stars, Amber Riley and Kevin McHale, urged fans to stop judging their fellow cast members who are yet to post about Rivera.
Other stars to pay tribute to Rivera include Jane Lynch, Chris Colfer and Kathy Griffin.
Rivera, 33, began her acting career at an early age and rose to global fame as cheerleader Santana Lopez in Glee, which ran on Fox from 2009 to 2015.
Rivera’s four-year-old son, Josey Hollis Dorsey, told investigators that his mother boosted him back on to the deck of their rented boat before he looked back and saw her disappearing under the water, authorities said.
“She must have mustered enough energy to get her son back on the boat, but not enough to save herself,” Ventura County Sheriff Bill Ayub said at a news conference.