This app was mentioned in 3 comments, with an average of 2.00 upvotes
Apps will usually use the location services available in the device. I have not used Bluestacks App Player, but try to see if there is any location settings.
Maybe an app for setting a mock/fake location will help. https://play.google.com/store/apps/details?id=com.tistory.maxxgreen.app.virtuallocation is one of these.
Personally from my testing experience, I'm probably going to stick to Virtual location unless I find something that actually fools Pokemon Go. It tricked my other apps just fine.
I am currently playing Pokemon Go in the most minimalistic sense of the phrase. I have tried using Bluestack's built in Location Service to emulate my location. I have tried using Virtual location, Mock Location, and a few others. These two are note worthy as I fully tested GPS reliant features of Bluestacks. I found that virtual location of both noted GPS Fakers successfully fooled both Google Maps and the Location Service built into the Bluestacks. However, neither of them got me off of Null Island.
My assumption is that Pokemon Go isn't taking our GPS location properly inside of Bluestacks. This might require stepin from a developer.