PyInstaller ImportError: No module named dateutil

What I run:

➜ pyinstaller --onefile app.py --hidden-import=dateutil

I use virtual environment to run everything and build. I already tried all variants of flags and etc. Doesn't work at all.

I get this error when im trying to open .app file:

Traceback (most recent call last):
  File "app.py", line 2, in <module>
ImportError: No module named dateutil
[4173] Failed to execute script app

Requirements:

➜ cat requirements.txt
numpy==1.15.0
pandas==0.23.4
python-dateutil==2.7.3
pytz==2018.5
six==1.11.0

I will be really happy if someone have any ideas how to solve it.