"The Internet is in most ways a great development for our society," Harper said at a roundtable on ways to protect youth from cyber-bullying.
"Unfortunately, it has other purposes and other uses, and young people are extremely vulnerable."
In order to better protect children from online threats, Harper said Ottawa is "expediting a review of the Criminal Code... to identify potential gaps with regard to cyber-bullying, cyber-intimidation, cyber-assault."
At the round-table event in Winnipeg, Manitoba, Harper was joined by the parents of two teenage girls who recently committed suicide after years of cyber-bullying and whose stories have provoked outrage in Canada and abroad.
Rehtaeh Parsons, 17, died in hospital last month in the port city of Halifax, Nova Scotia, after a suicide attempt that her mother blames on an assault and subsequent barrage of taunts by schoolmates calling her a "slut."
Parsons was said to have been drunk at a party when she was raped by four boys. One of the suspects later posted a photo of the incident online.
In a similar tragedy, 6,000 kilometers (3,730 miles) away in British Columbia province, Amanda Todd, 15, committed suicide last October after being tormented by an anonymous cyberbully.
In a YouTube video watched by millions worldwide, Todd said she "cried every night" after a photo of her breasts, flashed in an online video chat with a stranger a few years earlier, was distributed in her community in British Columbia. "I have nobody. I need someone."
After several failed suicide attempts involving cutting herself and drinking bleach and then posting the YouTube video describing her sadness, Todd finally killed herself on October 10.
Police investigated both cases, but no charges were laid.