Helm's wife Sandy and daughter Amy posted a message on his website on Tuesday (17Apr12) asking fans to send "prayers and love" to the stricken rocker, who is close to death.
Fonda worked with Helm on 1984 American TV movie The Dollmaker and she's opened up about her memories of him in a moving post on her blog.
She writes, "I got to know Levon personally because he played my husband in the ABC movie The Dollmaker. He was kind and deep and devoted to music, as a singer and playing not only drums, but harmonica, fiddle, mandolin, you name it.
"All you have to do is rent The Last Waltz, the documentary that Martin Scorsese made of The Band's last performance together to be reminded what an astonishing drummer Levon was.
"He gave the Band it's powerful, driving force, a wall of pulsating rhythm. And his voice - singing The Weight - all deep soul. I am so sad."