SACRAMENTO, Calif. — Attorneys general in Colorado and 16 states on Thursday urged the federal government to recall millions of Kia and Hyundai cars because they are too easy to steal, a response to a sharp increase in thefts fueled by a viral social media challenge. Some Kia and Hyundai cars sold in the United States over the last decade do not have engine immobilizers, a standard feature on most cars that prevents the engine from starting unless the key is present. Videos circulating on the social media service TikTok have shown how people can start Kia and Hyundai models by using only a screwdriver and a USB cable.