The accident happened on Friday in the Shah Khalid neighbourhood of Rawalpindi city, near the capital Islamabad.
Hamza Naveed, 18, was walking next to the tracks while a friend filmed him, Raja Rafaqat Zaman, a spokesperson for the local rescue agency, told AFP.
"The moving train hit him while he was posing for a video and walking on the railway track," Zaman said.
Rescue workers rushed to the site, he said, but the young man was already dead.
Friends of the young man told rescue workers he was posing for the video to post it on TikTok and his other social media accounts, Zaman said.
A police official at the local station confirmed the accident and other details.
Taking selfies and making videos for social media is wildly popular in Pakistan, as in other countries, with many youngsters using the posts to update their Facebook, Twitter and TikTok accounts.