The Internet removed both the distance between adherer of a specific political opinion and also the reluctance to openly express it. Also, it's all much faster and simpler to organize. So, yes, the alt-right surely has used the Internet, but that goes for all the others as well. The reason why the non-left as a whole (libertarians etc too) is maybe using the Internet more or better than leftists is because the cultural narrative is left. Television/entertainment is left, news are left, school/university is left - everything broadly follows leftwing ideas. That's why when you look for left stuff, you don't need the Internet, you can get that locally with well organized structures.

What I personally find problematic is the fact that the extremist right seems to be very crypto savvy and with every price hike of Bitcoin et al. Robert Spencer and his friends have a million more at their disposal. That is what everyone in the "sane" part of the spectrum of convictions should be concerned about (it's the same on the radical left with Soros money).