How do I toggle teammate visibility on the map?

The map screen has toggle buttons on the left side. A green icon means that group is shown, grey means hidden.

Teammates. Use the Teammates button.

Clanmates. Use the button with the clan shield. Every clanmate who's online and alive is shown on the map, however far away they are. When they're near you, you can also see them through walls. Clanmates aren't shown on the compass. The button only works if you're in a clan with at least two members.

You keep seeing your team and clan on the map while you're dead.

To see teammates at the edge of your screen when they're out of view, turn on Settings → Basic → Off-Screen Marker.