I need to test my app on different virtual devices

And another testing service with real and virtual devices that you can remotely control is testobject It is just for Android apps at the moment, but still a really nice tool to test with.

There's a few mobile app testing services that are available. These services include remote virtual access to most major devices available. Note these are real devices and some actually have live connections to some of the most popular telecoms.

Here are three of them:

Perfecto Mobile

KeyNote DeviceAnywhere

Less Painful

You need to weigh up how much virtual testing will achieve the desired amount of consistency you want between all possible device screens, testing on as much devices as possible would simply be a waste of your time because many devices have similar screen densities, resolutions and features that don't really effect how your view is presented unless you have placed your objects at static points. For example using pixel (px) measurements instead of density independent pixel (dp) measurements when setting your views.

My advice would be to set up about 10 AVD's with varying screen sizes, densities and features. Test your app on these and collate any oddities you spot between each device. If they are occurring at a specific resolution or screen density then you can begin to narrow down the possible reasons why the oddity is occurring.

Of course there isn't any real replacement for a physical device so the more physical devices you can test on the better.

If you need to test for specific devices, Samsung has a remote test lab, this way you can test real devices virtually and a large variety of devices.

Additionally, you can use the Amazon Device Farm which has Samsung phones as well as other Android, Fire, and iOS phones.