A 54-page report by the New York-based rights watchdog released in Tunisia said journalists in Libya are "assaulted, kidnapped and killed with impunity".
"Journalists were among the 250 people killed in apparent politically motivated assassinations in 2014," HRW said in the report entitled "War on the media: journalists under attack in Libya".
It also documented "at least 91 cases of threats and assaults against journalists, 14 of them women, from mid-2012 until November 2014", including 30 kidnappings and eight killings.
It said evidence suggests that "the armed groups sought to punish journalists and media outlets for their reporting, their opinions, or their perceived sympathies".
HRW blamed authorities for failing to protect journalists, and said this "has wiped out much of the limited freedom that existed following the 2011 uprising" that toppled and killed Kadhafi.
"Authorities failed to hold anyone accountable for attacks on journalists and media outlets since 2012," it said, while "courts are prosecuting people, including journalists, for speech-related offences".
The situation worsened last year sparking an exodus of journalists, said HRW, while those who chose to stay have been forced into self-censorship.
"Government authorities and non-state actors who control territory should urgently condemn attacks on journalists and where possible hold those responsible to account," he added in the report.
HRW researcher Hanan Saleh denounced a "culture of impunity".
"Many journalists don't want to report (aggressions they experienced) to the police because they don't think that the police or the judiciary can help them or do them justice," she told reporters in Tunis.
The North African nation has been wracked by conflict for the past four years, with rival governments and powerful militias battling for control of key cities and the country's oil riches.
