Every time I interact with any sub-21 year old person, I ask them 2 questions:
1.What's the most popular social network among your group of friends? I'd estimate 7-9/10 say Snapchat. If it is Snapchat, I proceed with question 2.
2.Do you read/interact with the "Discover" section of Snapchat? (Because this is where I think Snapchat has the most potential to actually make money.) I'd say 5-7/10 say Yes.
In short, yes, kids still use Snapchat.
A lot of people post everything to both, but Instagram usage has massively increased over the last few months.
Snapchat is still my go-to, but I've been peer pressured into posting Insta Stories as everyone else is now there.
Edit: Oh and I never use the Discovery page, neither do my friends. It's annoying and mostly useless.
You sound like a fun person - JK. But among my conservative, Midwestern sub-21 family and acquaintances, the answer was surging to Snapchat around Christmas. Then they moved lifestyle posts to Instagram, and moved communication/socializing back to Facebook. Also, they don't often interact intentionally with the Discover section.