"In my memory, she will always be vibrant and young. Gone too soon. Sending my thoughts and prayers to Amanda's family," Dempsey tweeted on Tuesday evening.
Peterson and Dempsey played love interests in the 1987 rom-com Can't Buy Me Love.The actress also appeared in A Year in the Life, Jack's Place, Silver Spoons and Doogie Howser, M.D. before quitting the business in 1994.
A cause of death for Peterson, who would've turned 44 Wednesday, hasn't been determined, but her father told TMZ that "she had some illness and a sleep apnea problem that may have contributed."