The protests started out peacefully and stayed peaceful for months, even in the face of state-sponsored gang violence (Yuen Long Station), false arrests, and police brutality. All of these things have rightfully angered the citizens of HK. They have every right to protest their government, especially the CCP, one of the most egregious violators of human rights in the modern era.
They are not just teenagers engaging in random street violence and property destruction. There are people from 12-80 on the street. Professionals, part-timers, students, retirees, everyone. Over a million people turned out last August in one of the largest protest marches in human history.
All the escalation is the result of CCP/HK not providing a political solution. They just send riot police to peaceful protests every weekend, and more violence occurs.
Admittedly it's hard to stay on top of all this stuff. The CCP's propaganda machine is working overtime and here in the West we're not doing a great job sounding the alarm in the press (in fairness, we have our own problems). But it's a serious protest movement fighting as honorably as it can for democracy and human rights, with global, fundamental consequences. We should be backing them 100%.