Amsterdam is a fun, free-spirited, laid-back city but, as in any other city, it's important to be street smart.
Areas in the city centre including Leidseplein, Rembrandtplein/Thorbeckeplein, Red Light District, Nieuwmarkt and the Haarlemmerstraat area draw a lot of tourists, especially for the nightlife, and are therefore often targeted by street dealers. It's important to ignore street dealers, do not buy drugs from street dealers. Do not engage them as they can be intimidating and violent.
Around 1,000 street dealers are arrested each year in Amsterdam. They are selling – mostly fake – drugs, act aggressively and steal money, passports and phones from tourists. Ignore them, always stay with your friends and never let them see where you keep your money or other valuables.