Cabello told fans that September 11, 2001 is a day "we will never forget" via her Instagram Story, while Witherspoon echoed the sentiment under a photo featuring a field of American flags.
"The heartbreak and devastation still overwhelm my mind," she wrote. "I promise to continue to pay tribute to the men and women who lost their lives and for the people who worked hard to save others."
Former "Glee" star Michele also shared a heartfelt post, sharing an image of the Twin Towers over a heart.
"A day we will never forget. 18 years later, and no matter where we are, we remember and honor all that we lost," she posted.
"Now that I've been living in New York I feel even more connected the city and have a truly heavy heart today," wrote Hudgens. "Sending so much love to everyone who lost a loved one and to everyone who worked tirelessly helping survivors."