1 second exposure and a quickly moving subject will get that.
Don't get too hung up on the "Rules Of Photography". If it's cool to you, shoot it. Now, do not mistake that with the "Fundamentals of Photography", those you should know and trust.
pretty neat. as mrpink said, a long exposure with the subject moving, or only spending part of the time in the frame will have that effect. some of my favorite night shots are like this. a couple of examples, hop you don't mind me high jacking your thread.
shutter: 25 seconds
ISO: 100
Fstop: 22
i was in frame probably 10-15 seconds of the 25.
shutter: 21 seconds
ISO: 100
Fstop: 16
i was in frame probably 15 seconds of the 21.
Bear in mind that it doesn't have to be the person who becomes transparent. It can be objects to. In this case, a stool underneath a person. This is one that me and my friends did, totally just screwing around a long time ago. Granted we could do way better now. Pardon the blue light, we couldn't find a normal flashlight.
No photoshop involved. But I could easily remove the rest of the stool if I felt like taking the time to do so.