Welcome to the game and to the forum. 
What platform do you have the game on and do you just have the base game or one or both expansions as well? It’s not easy to play base game with someone that has expansion/s. It can be done, but requires a bit of fiddling around to get it to work for the person with the expansion/s. Steam will probably have more multiplayers than GOG although you can now crossplay between the two.
We don’t have a dedicated multiplayer thread here since the game is mainly single player focussed, but you could also try over on the Grim Dawn Discord - they have a searching players channel there where you might find someone to play with.