As said, I'm no wealthy man or a politician or something like that, and I want to reach Moscow. Legally preferred, if not available, illegally. Were there transatlantic voyages available during war? After landing on France, how could I pass the Western Front, then hostile Germany, then Eastern front, then civil war ridden rural Russia, then to Moscow? How likely would I end getting killed or imprisoned?
I'm not familiar with how available transatlantic voyages were to average citizens at the time, but there would certainly be a lot of traffic since the US had just joined the war. If legal civilian passage was difficult, I'm sure it would be possible to find work on a transport ship and embark on the other end.
There would be many easier routes than passing through the western front and Germany. The allies had relatively solid control over the North and Baltic seas. If you could wait until winter ended, you could in theory take a boat straight to St. Petersburg.
If you wanted to play it even safer, you could go west and cross the Bering straight to Vladivostok. The Trans-Siberian railroad had already been completed, so it would be a straight shot.
Honestly the difficult part wouldn't necessarily be the western front so much as it would be getting through Russia. The Russian civil war would have just begun, and both St. Petersburg and Moscow were under Red Army control. The US was supporting anti-bolshevik groups (and even sent troops!) which would make things difficult and probably get you arrested as a spy.