Saying there were "further questions to be answered" by the tech giants, Ms Ardern said Facebook chief operating officer Sheryl Sandberg had been in contact and "acknowledged what has occurred here in New Zealand".
Ardern said there were "further questions to be answered" by the social media sites.
A horrific video shot by the gunmen who carried out the mosque massacre was live-streamed on Facebook before being removed by the company.
She was asked at a press conference whether Facebook should stop live-streaming, and said it was an issue she would look to discuss directly with Facebook.
"We did as much as we could to remove, or seek to have removed, some of the footage that was being circulated in the aftermath of this terrorist attack", she said.
"Ultimately, though, it has been up to those platforms to facilitate their removal and support their removal".
On Friday, YouTube tweeted it was "working vigilantly to remove any violent footage" while Twitter said it suspended the account of one of the suspects.
"Our hearts go out to the victims, their families and the community affected by this horrendous act", Facebook New Zealand spokeswoman Mia Garlick said in a statement.
Facebook has on its part said that as many as 1.5 million videos of the attack were removed from its platform in the first 24 hours.
New Zealand Prime Minister Jacinda Ardern speaks with a woman during a visit to the Canterbury Refugee Centre in Christchurch, March 16, 2019.
The distressing 17-minute livestream was available to watch on social media for hours after the attack that also left 34 people wounded.
He said "assurances were given" that once such content was pulled down, a regime would make sure it did not go back up.
Videos of the shooting appeared on all five platforms up to 10 hours after the attacks, which began at 13:45 local time in the city of Christchurch, Reuters found.
In another case, the video was shared by a verified Instagram user in Indonesia with more than 1.6 million followers.