The latest numbers are on par with what Pew researchers found last year but nearly double the 24 percent who said they were online almost constantly in polls conducted between 2014 and 2015.
The increase comes as experts and lawmakers have warned about the impact of social media on youth mental health.
U.S. Surgeon General Vivek Murthy released an advisory in May that argued social media use may be harmful to the mental health of young people, and Congress has been considering bipartisan proposals aimed at curbing social media harms for teens.
Black and Hispanic teens were more likely than white teens to say they are online almost constantly, according to Pew.
The poll found that 55 percent of Hispanic teens and 54 percent of Black teens said they were online almost constantly, compared to 38 percent of white teens who said the same.
There were also differences between age groups of teens. While 50 percent of teens ages 15-17 said they were online almost constantly, 40 percent of teens 13-14 said the same.
Nearly all teens — 95 percent — said they have access to a smartphone, and Pew found that smartphone ownership is “nearly universal” among teens of different genders, ages, races and ethnicities, and economic backgrounds.
Among U.S. teens, YouTube remains the most widely used online platform, followed by TikTok, Snapchat and Instagram.
Some 93 percent of teens said they use YouTube, while 63 percent said they use TikTok, 60 percent said they use Snapchat and 59 percent said they use Instagram, the survey found.
Facebook and Twitter, now known as X, have declined substantially in popularity among teens in recent years. Only 33 percent in the Pew poll said they use Facebook, while 20 percent said they use X.
Read more in a full report at TheHill.com.