More than half a million users have piled onto the Chinese social media platform Xiaohongshu, also known as RedNote, days ahead of a looming ban on TikTok in the United States, according to data from app stores and social media videos. Styling themselves “TikTok refugees,” many young Americans, seeking an alternative to TikTok, are flocking to join RedNote’s 300 million existing users -- who are mostly in China -- taking what they see as refuge from the ban, which could be enforced on Jan. 19.