As you know, many A-listers posted online in the hours after news of the One Direction alum's death in Argentina broke Wednesday. As word of Liam's fatal fall spread across the globe, more and more stars are paying tribute to the late singer.

Halsey posted on her Tumblr Thursday, where she confirmed she was a devoted Directioner during 1D's heyday. She wrote ... "As a parent, a fellow artist, and a fan, i simply cannot fathom this untimely loss. my heart goes out to his family, friends, and the fans."

Camila Cabello, who, like Liam, got her start in the music industry thanks to "The X Factor," recalled meeting the singer at a young age on her Instagram Stories. She added ... "It's a tragedy to have him gone way too soon."

As we reported, Liam's One Direction bandmates -- Harry Styles, Louis Tomlinson, Zayn Malik, and Niall Horan -- issued a poignant statement from their band's Instagram account. In their joint statement, the group shared they are "completely devastated" by the tragic update ... noting their memories with Liam will be treasured "forever."

Zayn and Louis also issued their own separate statements, where they each expressed the extent of their grief.

The Backstreet Boys, another world-famous boy band, addressed Liam's death ... sending their condolences to the singer's family, friends and fans.

Quavo, The Wanted's Max George, Olly Murs, and many others have posted equally touching tributes.

There have also been notes from those within One Direction's close circle ... including Harry's mom, Anne Twist, Niall's brother, Greg, and 1D guitarist Dan Richards.

Liam was pronounced dead at the CasaSur Palermo Hotel in Buenos Aires, Argentina Wednesday after falling from the third-floor balcony of his room. The singer allegedly had a meltdown before his fatal fall ... this according to the 911 call made prior to his death.

Liam is survived by his son, Bear, who he shares with ex Cheryl Cole.