Everyday Warnings: You will frequently see or hear warnings like `小心小偷 (xiǎoxīn xiǎo tōu)`, meaning “Be careful of thieves/pickpockets,” in crowded public places like subways, train stations, and tourist attractions.
Describing a Crime: It's the standard word used when telling someone your wallet, phone, or bag was stolen. For example, “My phone was taken by a `小偷`.”
Media and News: News reports about shoplifting, pickpocketing rings, or residential burglaries will almost always use the term `小偷`.
Connotation: The term is overwhelmingly negative and serious. However, in a very informal and playful context, you might call a pet or a child who sneakily takes food a “little thief” (`小馋猫,像个小偷一样 - little greedy cat, just like a little thief`), but this is a metaphorical extension of its core negative meaning.