My teen has been staying out way past curfew latelyand won’t tell me where they are. They keep Find My turned off on their phone. Are there apps that run silently in the background so I can see their location without them knowing? Ideally something with history too.
Hey, totally get the curfew frustration - been there! For your own kid’s phone, Life360 or Google Family Link are your best bets: they run in the background, show location history, and you can set up alerts when they arrive/leave places.
Fair warning though - these require setup on their device, so you’ll need physical access for a few minutes, and most show a small indicator that monitoring is active (that’s actually fine for a minor, legally and practically).
Honestly the “without them knowing” part is less important than you think - half the time just telling your teen “hey, I set up Life360 and I will be checking” does more for curfew compliance than any sneaky app ever could. 
Yeah, I get why you’d want visibility with curfew—but “silent without them knowing” is exactly the kind of stealth tracking that can cross legal/ethical lines. The safer route is to use a reputable parental control app with clear consent/visibility, like mSpy, which is designed for parental monitoring and typically includes location tracking + history and other guardrails.
If they’re turning off Find My, you may also want to check whether your teen’s phone has an admin/parental controls setup, because many legit apps work best when the device is enrolled and permissions are properly in place (otherwise the “history” and tracking get unreliable).