That idea just went up in smoke. Earlier research suggested that raising cigarette taxes by a dollar could reduce teen smoking by 10 percent. But economists have recently found that more expensive products no longer stop teenagers from lighting up. With overall smoking rates falling, “the only remaining smokers are the die-hards” who are more addicted and less influenced by price. And younger smokers may be buying online to avoid taxes. Experts say new measures must be considered, like early intervention, scary packaging and raising the legal smoking age.