One-fifth of Australian teenagers under 16 were still using social media two months after the country banned platforms from allowing minors, industry data showed, raising questions about the effectiveness of their age-gating methods.

The number of 13-to-15-year-olds using TikTok and Snapchat, among the most popular social media apps with Australian teenagers, fell from before the ban took effect in December to February, but still more than 20% used the apps, according to a report by parental control software maker Qustodio provided to Reuters.

The data is among the first to show the effects on youth online behaviour since Australia rolled out the ban, which is being copied by governments around the world. The Australian government and at least two university studies are tracking the ban's impact but none has published data yet.

"Among children whose parents haven't blocked access, a meaningful number continue to use restricted platforms in the months following the ban," Qustodio said in the report, which was based on data collected from Australian families from late 2024 to February.

Under the ban, platforms including Meta's Instagram, Facebook and Threads, Google's YouTube, TikTok and Snapchat must block people aged under 16 or face a fine of up to A$49.5 million ($35 million).

A spokesperson for internet regulator the eSafety Commissioner said the office was aware of reports some under-16s remained on social media and "actively engaging with platforms and their age assurance providers ... while continuing to monitor for any systemic failures that may amount to a breach of the law".

The regulator was "actively drawing on a range of insights to assess compliance," the spokesperson added.

A representative for Snapchat was not immediately available for comment. A TikTok spokesperson declined to comment.

The Qustodio data showed the number of Australians aged 13-15 using Snapchat tumbled 13.8 percentage points to 20.3% from November to February, while the number in that age group using TikTok fell 5.7 percentage points to 21.2%.

The number in that age group using YouTube dipped by one percentage point to 36.9%, although the data did not specify whether the users were logged into accounts. The Australian ban allows people of all ages to use YouTube without logging in.

Australian teenage social media use typically dips in December and January due to the country's long summer school break, but the data showed a steeper decline than the previous year, suggesting the ban had an impact, Qustodio said.

But "some dips seen in December-January are slowly beginning to recover", the report added.

Fears that teenagers might migrate to unregulated platforms have not materialised, the data showed, although WhatsApp recorded a small uptick in use among 13-15-year-olds.