A conservative commentator who sent a tweet saying he would use “a hot poker” to sexually assault an outspoken 17-year-old survivor of the Florida high school shooting has resigned from a St Louis TV station and been taken off the radio after several advertisers withdrew from his shows.

KDNL-TV accepted Jamie Allman’s resignation and canceled The Allman Report, according to a brief statement from the Sinclair Broadcast Group, which operates the TV station. Before the show’s launch in January 2015, KDNL-TV touted it as a nontraditional newscast with a conservative spin.

Allman’s radio show on KFTK-FM has been taken off the air while the company “looks into the matter”, said Esther-Mireya Tejeda, a spokeswoman for Entercom, which began operating the station last month.

Allman hasn’t responded to messages seeking comment.

Several businesses pulled advertising from Allman’s shows after he sent the 26 March tweet targeting David Hogg, who has strongly advocated for stricter gun control since 17 people were killed in the 14 February mass shooting at his school in Parkland, Florida.

In the tweet, Allman wrote: “I’ve been hanging out getting ready to ram a hot poker up David Hogg’s ass tomorrow.”

Allman’s Twitter account was “locked” shortly after he sent the tweet, restricting access to his account, but a screenshot of it has been widely circulated on social media.

Hogg’s willingness to take on the gun-control cause has made him a target for some conservatives. Fox News Channel’s Laura Ingraham took a week’s leaveafter apologizing via social media for her tweet saying that Hogg had “whined” about not getting in to some colleges.

Another student, Emma Gonzalez, has been falsely depicted in a doctored photo tearing up the Constitution.

Sinclair is a conservative-leaning company that owns nearly 200 local TV stations, making it one of the largest such companies in the US.

Donald Trump last week defended the company after a video showing dozens of Sinclair news anchors reading a script expressing concern about “fake stories” and “one-sided news stories plaguing the country” appeared on TV news reports and circulated online. Trump said rival TV stations were merely “worried about the competition and quality of Sinclair Broadcast”.

Sinclair also has pushed for regulation of the broadcast industry to be eased and is trying to buy Tribune Media in a move that would dramatically increase the company’s reach.