"Congressional action is needed. They won't solve this crisis without your help," she added.
In her testimony, she noted the danger of the power in the hands of a service that is woven into the daily lives of so many people.
"The company intentionally hides vital information from the public, from the US government and from governments around the world," Ms Haugen's statement said.
She spoke less than a day after Facebook, its photo-sharing app Instagram and messaging service WhatsApp went offline for roughly seven hours, hitting potentially billions of users and highlighting global dependence on its services.
"Here's my message for [Facebook CEO] Mark Zuckerberg. Your time of invading our privacy, promoting toxic content and preying on children and teens is over," Senator Ed Markey said.
"Congress will be taking action... we will not allow your company to harm our children, our families and our democracy anymore."
Facebook harms children and weakens democracy, claims whistleblower
Senator Amy Klobuchar said she sees the whistleblower disclosures as the long-needed push to get Congress moving.
"I think the time has come for action, and I think you are the catalyst for that action," she told Ms Haugen.
US lawmakers for years have threatened to regulate Facebook and other social media platforms to address criticisms that the tech giants trample on privacy, provide a megaphone for dangerous misinformation and damage young people's wellbeing.
Facebook has pushed back hard against the whistleblower revelations and attacked Ms Haugen's knowledge on Tuesday.
Ms Haugen "did not work on child safety or Instagram or research these issues and has no direct knowledge of the topic from her work at Facebook," tweeted Andy Stone, a spokesman for the company.
Facebook blames global outage on 'faulty configuration change'
Ms Haugen, a 37-year-old data scientist from Iowa, has worked for companies including Google and Pinterest, but said in an interview on Sunday with CBS News' 60 Minutes that Facebook was "substantially worse" than anything she had seen before.
Facebook's vice president of policy and global affairs Nick Clegg vehemently pushed back at the assertion its platforms are "toxic" for teens, days after a tense, hours-long congressional hearing in which US lawmakers grilled the company over its impact on the mental health of young users.
Facebook late on Monday blamed the outage on configuration changes it made to routers that coordinate network traffic between its data centres.
"This disruption to network traffic had a cascading effect on the way our data centres communicate, bringing our services to a halt," Facebook vice president of infrastructure Santosh Janardhan said in a post.
In addition to the disruption to people, businesses and others that rely on the company's tools, Facebook CEO Mark Zuckerberg took a financial hit.
Fortune's billionaire tracking website late Monday said Mr Zuckerberg's personal fortune plunged by nearly A$8.2 billion (US$6 billion) from the prior day to land at A$160 billion (just under US$117 billion).
Some people rejoiced at Facebook's tools being offline, but some complained to AFP that the outage had caused trouble for them both professionally and personally.
"I love Instagram. It's the app I use the most, especially for my job," said Millie Donnelly, community manager for a non-profit.
"So professionally, it's definitely a step back and then personally, I just am always on the app."