Stars including Lady Gaga, Miley Cyrus, Matthew Mcconaughey, Chloe Grace Moretz, Ben Stiller and the Jonas Brothers have joined millions across the world in marking the 12th anniversary of the 9/11 terrorist attacks in America. Nearly 3,000 people were killed on 11 September, 2001, after two hijacked planes were flown into the World Trade Center in New York City, while a third plane ripped into the Pentagon military defence headquarters in Virginia and another went down in Pennsylvania. A ceremony was held in New York City on Wednesday morning (11Sep13) to mark 12 years since the atrocities, and a number of celebrities marked the anniversary in posts on Twitter.com. Pop star Lady Gaga, who was brought up in the Big Apple, writes, "12 years ago today Sept 11th. We will never forget. Still remember the smoke in the sky. Saying lots of prayers for families who lost lives." The Jonas Brothers wrote, "Never forget. 9/11" while Kings of Leon rocker Nathan Followill adds, "Remembering those who were taken too soon on this date 12 years ago. Sad day for all but stronger than ever. Never Forget." British musicians Duran Duran posted, "Our thoughts are with every one who was affected by the tragedies of 9/11. We hope that all reading have a day filled w/ (with) peace," and music mogul Simon Cowell reached out to the victims' relatives: "My thoughts are with the families who lost someone special. They will never be forgotten." Singer/actress Miley Cyrus threw her support behind a campaign which urges members of the public to do a good deed to mark the sad occasion, writing, "Do a good deed today in observance of 911 Day. Make your pledge at 911day.org." Missy Elliott marked the day by recalling her time in New York City on the day of the attacks, writing, "I remember 9/11 like it was yesterday. I was in NY just did (a) Michael Jackson tribute the night before... Me and Nelly Furtado performed. She made her plane but I got stuck in NY for days during 9/11 they closed everything... Many Prayers for the families grieving over the loss of a loved one during the 9/11 tragedy. May they rest in peace. Never 4gotten (sic)." Actor/director Ben Stiller adds, "Glad to be in NY on 9/11. Remembering all those who lost someone." Other messages came in from Josh Groban, Spike Lee, Mena Suvari, Sheryl Crow , Bobby Brown, Julianne Hough and Chely Wright, while actors Matthew McConaughey and Chloe Grace Moretz both posted photo tributes. A number of other stars are raising money for good causes on Wednesday by manning the phones on trading floors in both London and New York as part of the annual Cantor Fitzgerald and BGC Partners' Charity Day.