Seien-dan
According to the official website, seiyu Inoue Kazuhiko has organized a group of seiyu "Seien-dan" to give cheer to the victims of the earthquake. Twenty-eight seiyu have joined Seien-dan. Sixteen of them recorded a rooters' song written and composed by Inoue and uploaded it on Youtube on March 19th.

Kimitachi ni Okuru Ohenka ("Rooters' Song For You", Youtube)
Singers of the video:
Inoue Kazuhiko, Chiba Chiemi, Kanai Mika, Katsu Anri, Ito Kentaro, Koganemaru Yamato, Sanada Asami, Sawashiro Miyuki, Canna Nobutoshi, Takahashi Naozumi, Okiayu Ryotaro, Konishi Katsuyuki, Seki Tomokazu, Hoshi Souichiro, Shocker OH!NO!,Orikasa Fumiko

Seiendan uploaded another video on March 22nd. It recorded the messages of all the twenty nine members.

Messages from Seiendan (Youtube)
Thirteen additional members:
Asano Masumi, Fukuen Misato, Matsuzaki Akiko, Kobayashi Yumiko, Saiga Mitsuki, Terashima Takuma, Nagasawa Miki, Fujita Saki, Mitsuishi Kotono, Morikawa Toshiyuki, Morikubo Showtaro, Yamaguchi Kappei, Paku Romi

Source: Inoue's blog

Message from Tessa
Seiyu Yukana announced in her blog that she had uploaded a message video from Tessa, a character of Full Metal Panic!. The lines were written by Gatoh Shoji and the illustration was drawn by Shiki Douji.

Message from Tessa (Youtube)

Source: Yukana's blog