Cher, Cyndi Lauper, Lena Dunham and Zach Braff are among the stars who have joined the call for tighter gun control laws in the U.S. as America reels from the massacre at a Connecticut elementary school on Friday (14Dec12).

A gunman, named as Adam Lanza, 20, opened fire at Sandy Hook Elementary School in Newtown, killing 20 kindergarten students. Reports suggest the shooter then turned his gun on himself. A total of 28 people were killed in the shooting rampage, including Lanza's own mother, who was a teacher at the school.

As news of the deaths hit headlines, stars took to social networking sites to express their horror at the tragedy - and many are taking aim at America's National Rifle Association (NRA) and calling for officials to overhaul gun laws.

In a series of angry posts on her page, pop superstar Cher writes, "How many times do we have 2 (sic) hear 'gunman kills'. Fk (f**k) The NRA! They put money above your children's lives. Guns kill people, little innocent 1's (sic).

"We cant cure gun violence completely, but we can bring it down to the LEAST Murders by Gun in a Civilized Country! I know people kill people, but HOW MANY FEWER CHILDREN WOULD THIS CRAZY MAN HAVE KILLED WITHOUT HIS THREE fkng (f**king) GunNNNNNNNS (sic). He couldn't have done this kind of damage without 3 guns, multiple clips &tons of ammunition no matter how crazy he was."

Actor Braff ‏added, "No one is saying you can't have your gun, crazy angry gun guy. But most of the country is tired of how easy it is to get a gun. Sane people, we mustn't let up on our politicians when this tragedy fades front the top story. This time lets not get silenced by the NRA", while Lauper lamented, "Really so sad today in Ct (Connecticut). Why does it have to be so easy to carry guns? Just so sad all the way around."

Girls star Dunham posted a link to an article calling for tighter gun control, and added: "What happened today in Newtown is unspeakable on every level. Let's do more than grieve...", and actress Sophia Bush wrote, "We need to reform our laws AND our way of thinking. It shouldn't be easier to get a gun than to get mental health care."

Actor Sean Astin ‏told his followers, "The last minutes of this awful day pass... My anger about gun violence & failures regarding related mental illness challenges rages in my soul".

Meanwhile, several stars continued to share their grief over the tragedy - Justin Bieber tweeted, "heard about what happened in Ct, my prayers go out to all those suffering in this tragedy. it's just wrong. Everyone please pray for them".

Olivia Munn added, "My heart is broken for the parents who waited for a reunion with their children today, only to find out that they will never get one"; Kathy Bates ‏declared, "PrayForNewtown. For the precious souls slaughtered today and for their shattered loved ones who will mourn for all the days to come", and Michael Jackson's daughter Paris simply stated: "Sitting here watching the news..... this is killing me."

Actor Wilmer Valderrama reveals he was left stunned by the massacre, writing in a series of posts, "As I flew across the country, I took time to process the horrible nightmare we as a nation lived this morning.. I am lost for words.. We've endured some painful catastrophes.. Today.. I feel so heart broken at the helplessness of these things happening...To the families & everyone affected directly & indirectly .. We stand by you and pray with you.. God please give them light."

Connecticut-born James Van Der Beek tweeted, "My heart breaks for my home state... Going to stop trying to make sense of anything today and just grieve & send love along with the rest of the country", and Gloria Estefan ‏told fans, "My heart break (sic) for the parents, families & friends of the victims of the Newtown shooting! Praying for them, for us, for country & our world! If we can fund maximum security prisons, we should be able to create maximum security schools".

The world of rock also mourned the deaths - Travis Barker wrote on Twitter, "Holding my family really close tonight. Praying for all those lost in the Newtown Connecticut shootings and their families. My heart goes out to all of a father this is just heartbreaking. Makes me sick to my stomach. May the person responsible rot in hell"; Slash shared, "The Conn elementary school shooting is horrific. Those poor kids. & their families. I'm speechless"; and Kings Of Leon rocker Nathan Followill, who is set to become a parent in the coming weeks, added, "Just saw the tragic news about the school shooting. As a soon to be father this is tragic. My thoughts & prayers are with the families."