The stock fell as low as $30.62 by the end of trading, down more than 12 percent for the week.
Dorsey testified before two congressional committees Wednesday to address online election interference and claims of political bias on the platform. They're familiar conversations for Twitter by now, as scrutiny of social media companies heightens ahead of the midterm elections in November.
Facebook, Twitter and Google have all ramped up detection efforts in light of calculated foreign misinformation campaigns during the 2016 presidential election. Twitter said last month it removed hundreds of abusive accounts, many of which had ties to Iran.
At the same time, Twitter is answering to accusations from prominent Republicans of conservative censorship. President Donald Trump has called the company's actions "discriminatory and illegal" and vowed to look into the matter. The Department of Justice said Wednesday that Attorney General Jeff Sessions would be meeting with state officials later this month to discuss growing concerns around tech companies.
Dorsey is less familiar with the spotlight, though. He said during prepared testimony Wednesday he's "typically pretty shy."
Lawmakers and insiders commended Dorsey for his candor and apparent off-the-cuff answers during the back-to-back hearings. But it appears Twitter shareholders were harder to win over.
As of close Thursday, the stock is on pace for its worst week since July when it shed 20 percent on a disappointing earnings report.