Data from app monitoring firm App Annie indicates that average time per user spent on the apps is higher for TikTok, indicating high levels of engagement.
App Annie characterised TikTok as having "upended the streaming and social landscape".
However, YouTube retains the top spot for overall time spent - not per user - as it has many more users overall.
The Google-owned video giant has an estimated two billion monthly users, while TikTok's most recent public figures suggested it had about 700 million in mid-2020.
App Annie specialises in analysis of the apps market.