NEW YORK (AP) — TikTok, an app best known for dancing videos with 1 billion users worldwide, has also become a shopping phenomenon. National chains, hoping to get TikTok’s mostly young users into its stores, are setting up TikTok sections, reminiscent of “As Seen On TV” stores that sold products hawked on infomercials. The hashtag #TikTokMadeMeBuyIt has gotten more than 5 billion views, and the app has made a grab-bag of products a surprise hit: leggings, purses, cleaners, even feta cheese. Brands are often caught off guard. TikTok wants a cut of those viral product sales and is gearing up to challenge Facebook as a social-shopping powerhouse.