"For the last seven years the 13th of July has shattered our hearts beyond repair," she wrote. "There aren't enough words to describe the pain we are feeling, we are truly heartbroken at the loss of @nayarivera.
"Naya, Cory loved you so, so much. He cherished your friendship more than you will ever know. From the laughs you shared, to the strength you gave him when he needed it the most. Cory truly adored you.
"He was in awe of your incredible talent, the way you gave everything you had to each performance; the slap in the auditorium was one of his favourite stories to share. You once said Cory was like a member of your family; you will always be a part of ours. We'll carry you in our hearts forever. We miss you. Friends reunited for eternity.
"We send all our love and strength to your beautiful boy, your family, friends and fans," she wrote.
An autopsy revealed earlier this week that Rivera died of accidental drowning.
Rivera rented a pontoon boat on Lake Piru, which lies inland 100km northeast of Los Angeles, at about 1pm last Wednesday with her son, Josey Hollis Dorsey.
The boat rental company went searching for the pair when Rivera didn't return the vessel on time, and discovered Josey asleep and adrift on-board.
"We know from speaking with her son that he and Naya swam in the lake together at some point during their journey," the Ventura Country sheriff said.
"It was during that time that her son described being helped into the boat by Naya who boosted him onto the deck from behind. He told investigators that he looked back and saw her disappear under the surface of the water.
"There are a lot of currents on the lake that appear particularly in the afternoon. We believe it was mid-afternoon when she disappeared.
"The idea being perhaps that the boat started drifting, it was unanchored, and that she mustered enough energy to get her son back onto the boat but not enough to save herself."
Rivera's body was located in the same area where she went missing.