Participating organizations include Public Campaign, Occupy the NRA, CREDO, Every Child Matters, Moveon, United For Change, USA, New Yorkers Against Gun Violence, The Other 98%, and We Act Radio.The article has pictures showing what is says is generously 100 people, including reporters. There is supposedly a vast majority of Americans who support gun control, but much of that support is for laws that are already on the books,* and much of the rest is very mild support. Even among liberals (other than mainstream media employees) this support isn't spectacularly strong.
*Some years ago, one of the respected polling organizations in California asked Californians what sort of laws they would support. They found a strong majority supported a ban on mail order sales of guns. At that point, it was more than 25 years too late to pass such a law, because the Gun Control Act of 1968 had already done that.