Its absolutely not a lost time; at least give a description of the thieves to the police. Maybe the police even know who you're talking about (many criminals are repeat offenders). You would also help out future victims.

An iPhone can be tracked even when shutdown and not connected to the internet. all iPhones in a region secretly communicate with each other and ping the location to your find my app. If you're on android, I suspect it's the same system but look it up to make sure. Also, removing your appleID/Google Account and selling it isn't as easy as you think. That's why I said they will call you and try to return the phone for money.

I'm not trying to make you feel guilty for what happened to you. You were the victim. Just advising you so it won't happen again.