Sia, Melissa Etheridge and k.d. lang are among the celebrities participating in Billboard's Love Letters to the LGBT Community campaign.

“We flow. Continually,” wrote Lang, who came out lesbian in 1992. “Becoming a beautiful diverse current that winds its way toward an ocean of human equanimity and openness. Every single one of us contributing to the flood. I'm proud to be by your side in this great melt.”

Sia, who is bisexual, said that without question she wouldn't have made it without her queer friends.

“I am forever grateful to God for creating them in all their glory,” the Australian singer wrote.

Melissa Etheridge thanked her LGBTQ fans.

“Thank you to my LGBTQ fans that make me a better person every day,” she wrote. “Brothers and sisters (and everyone in between) I love you with all my heart and I will forever be grateful.”

(Related: Adam Lambert “blown away” by progress of LGBT community.)