[Help] - Which Ad Network Is Best For European Visitors

Hi all.

I am pretty new to the Android App arena and am learning a lot very fast here so might be missing something.

I have an app live that is now getting a good level of traffic and I have been looking to monetize it.

I have currently got accounts with MobFox, Admob & LifeStreetMedia in a stack in MoPub but they are rarely serving any ads so it is always serving my back-fill ad.

I am thinking this is because 90% of my traffic is people in Europe and many of the advertisers are looking for US visitors?

Can anyone recommend any ad networks that might be better suited to me? My app is in the football (soccer)/sports/gambling niche!

Any help gratefully received.