There are two ways how to get in touch with your friends. Please note that it is not possible to play with your friends in case you have not connected your game to either your Facebook profile or your Pixel Portal account.

In case you are playing the Trainstation game via the Trainstation app, you can connect your game to your email address after visiting your Settings and selecting the Option Login with email. You will be prompted to create an email Login for your game afterwards.
Once you complete this action, you will be able to befriend players on the Pixel Portal - https://portal.pixelfederation.com/en/
After visiting your profile at Pixel Portal, you will be able to search for friends and befriend them. You can either use their email address or their Pixel ID in order to locate them via the Search tool.

If you would like to connect your game to your Facebook, but you have been playing your game already and have achieved some progress and you would not like to loose this progress, please reach out to the Support Team in order to have your game synchronized. Unfortunately, if you would select the option to connect your game to Facebook, it would be overwritten with the Trainstation game level and progress which is currently active on your Facebook (most of the time it is at level 0). You will not be able to access your old game afterwards and you are risking the loss of your game by completing this action, as it is not always possible to locate the lost game.

After your game is connected to your Facebook account, please check if you have allowed TrainStation and Pixel Federation access to your friend list
You will be able to see and invite your Facebook friends afterwards.