Speaker of the House Paul Ryan's tweet, in which he said, "The people of Sutherland Springs need our prayers right now" was met with responses from celebrities, academics and others.
Actor Jimmi Simpson called out Ryan specifically, tweeting "your actions could've prevented it."
The hashtags #guncontrol and #guncontrolnow were also trending in cities around the U.S.
Sen. Elizabeth Warren of Massachusetts called for action against "letting the NRA control this country's gun policies."
Former President Barack Obama also called on people to think about what steps they can take to reduce violence.
At least 26 people were killed and 20 others injured when a gunman opened fire at the First Baptist Church during Sunday morning services.
The shooter. identified as Devin Kelley, 26, of New Braunfels, Texas, is also dead.