Here's some interesting public polls (Gallup): https://news.gallup.com/poll/237818/young-people-adopt-vapin...

According to their data, in the 18-29 demographic, 20% vape compared to 16% using traditional cigarettes.

And some analysis from the academic side: https://tobaccocontrol.bmj.com/content/early/2018/10/31/toba...

"There was a substantial increase in youth vaping prevalence beginning in about 2014. Time trend analyses showed that the decline in past 30-day smoking prevalence accelerated by two to four times after 2014. Indicators of more established smoking rates, including the proportion of daily smokers among past 30-day smokers, also decreased more rapidly as vaping became more prevalent...

The inverse relationship between vaping and smoking was robust across different data sets for both youth and young adults and for current and more established smoking. While trying electronic cigarettes may causally increase smoking among some youth, the aggregate effect at the population level appears to be negligible given the reduction in smoking initiation during the period of vaping’s ascendance."

So, it seems to be mixed. Certainly more younger folks vaping than using cigarettes, though it's roughly 55%/45%... and this might not have a strong impact on overall smoking rates.

(I'm actually surprised. I expected to see more vape use based on my own anecdotal observations!)