Why does AC pass through my body if I touch a hot wire? Is there a closed circuit created?

I answered this SE EE question two hours ago.

My answer

A very popular (especially in the past) application of this phenomenon is the neon-lamp line tester. Its operation is surprising and incomprehensible to many people, because at first glance it does the impossible - it measures the voltage with just one probe!

For the participants in this discussion, the answer is clear - a very weak (but enough to light the neon lamp) current flows mainly through the capacitive coupling and leakage of the human body to the ground. So the human body acts as the other probe. See also How does a "neon tester" work?

I remember that in the past I had noticed an interesting detail - the tester did not work well (the neon lamp glowed very dimly) when I tried to measure the voltage while standing on a ladder. Guessing about its operation principle then I used a simple trick - I touched my other hand to the wall... and the lamp glowed brightly.

But later I realized that this is dangerous because the built-in resistor is quite unreliable (they usually make it from some pressed graphite mass). So don't do that!