Here are a couple of possibilities:

• When I try focusing with the electronic viewfinder I find it helpful to zoom in on the live view. (Not sure if your camera can do that)

• Depending on your scene, you can also use a torch to light the scene as focusing aid. If the subjects are too far away, use knowledge of hyperfocal distance to focus on something that is within the reach of your torch or laser pointer.

• And I would not just put the focus to "infinity" as with most lenses that position is actually focusing beyond infinity most of the time. However as a last resort, you can always start at "infinity" and move the focus point by trial and error.

Update: Okay, here is my final advice after running into similar problems and the tips from my previous answer failed:

First thing is to find out where the actual infinity position is on your lens during daytime. Once you know that (on my Sigma its actually where it should be..) you can manually focus to that position at night.

The second thing is to shoot at high f-stop numbers, where the exact focus isn't that important for a sharp picture.

If everything else fails you can always come to your scene earlier and use your auto-focus with the available light. :-)