Even if you get their IP, dafuq are you going to do with it.. Just use their instagram name and link as many things to it as possible but generally, if you found someone on instagram it's kinda the end result of finding who someone is :\
If you know them and they trust you enough to click a link you could just do that sent up a short url that keeps ip's
There's websites that allow you to do this. I used to do it all the time on Omegle. But in this day in age, having somebody's IP to phish for information is useless as almost every mobile phone and most WiFi routers are run through Google Public DNS or OpenDNS now. The most you can do is DDOS them.