I think peer pressue does play a large role. If everyone is copying someone (& presumably it’s the “cool kids”)the question remains- what causes the desire for any of them to start.
My guess would be the need to escape. Nicotine acts in the brain to stimulate feelings of pleasure. It also will work as an appetite suppressant and can relieve stress. Experimental smoking usually begins the habit. Next comes occasional cigarette smoking at parties, on weekends, with friends or when trying to lose weight. This is the most dangerous stage, because it usually leads to an addictive phase, when teens become regular smokers