This is a question that is rooted in personal experience. I do not know if there are any statistic available to verify this. However, from a common sense point of view, we can say that it is stressful being a teenager these days for several reasons.
First, there is a breakdown of the idea community. So, in the past the community would help raise people. But now there safety net is no longer there. In other words, the rise of individualism leaves people alone, teens included.
Second, times are getting more competitive. So, there are fewer spots in all areas that teens are competing for. This will produce stress. Think of college admissions and how competitive things are getting.
Finally, I would argue that we have had it good for a while now. For this reason, there are certain expectations that teen have. This creates a certain mentality and when challenges comes, it is harder to cope with them.