Sad news has surfaced again in the festival world. In Hasselt, Belgium, a stage collapsed during the first day of the annual Pukkelpop festival -- where 30 Seconds to Mars, Good Charlotte, Foo Fighters, Eminem were set to perform -- leaving multiple casualties. This follows the tragic news from last weekend, when a stage collapsed at the Indiana State Fair and killed five people. Fans, as well as pop stars, have been sending the Twittersphere ablaze with heartwarming notes and condolences. 30 Seconds to Mars, OneRepublic, Travis Barker and more have already sent tweets to those affected by the incident. Read all of the artists' thoughtful messages below.