Pedro Pascal, Constance Wu & More Stars Pay Tribute to Catherine O'Hara

Catherine O'Hara's death has spurred numerous celebrities to share loving posts about the iconic star ... with Pedro Pascal, Constance Wu, LeAnn Rimes, and more taking part.

Stars are posting older pictures of O'Hara ... sharing their feelings of heartbreak and -- in the case of Wu -- calling her one of her generation's finest actors.

Pascal shared a photo with O'Hara from the set of "The Last of Us" ... with the two embracing and grinning for the camera.

Pedro says his world's a bit darker now that O'Hara is gone ... before calling her the "one and ONLY" Catherine O'Hara.

Andy Cohen shared a picture of O'Hara from the Canadian sketch show, Second City Television, on which many other big names -- like Martin Short and John Candy -- got their big break. Cohen says he "fell in love" with O'Hara after first seeing her on the show.

"It's Always Sunny in Philadelphia" star Kaitlin Olsen shared her grief, as did Lea Thompson, Katie Maloney, Lisa Ann Walter, and many more, who also paid tribute to her -- so did her "Home Alone" son, Macaulay Culkin.

We broke the story ... O'Hara died Friday morning after she was rushed to the hospital after paramedics were called to her home. According to dispatch audio, O'Hara was having trouble breathing.

Her cause of death is currently unknown. She was 71 years old.