Tap the Friends icon in the lower left corner of the screen. In the pop-up window you’ll find a tab with an exclamation mark. All your friends currently asking for help are listed there.

You can also help other players who are not your friends. Go to the Find friends tab to look for players who need help: you can find them by looking for images with exclamation points.

When you enter the towns of players who need help, an exclamation mark will also appear next to their icon and a help request icon will appear over their railroad station or airport.

Once you enter a co-op, you'll see your fellow members request products in the co-op chat. Tap Help if you'd like to respond.