Indicators: Avoids eating in front of people, made very uncomfortable by being forced to eat, (not always) major weight loss, lack of interest in daily things, lack of energy, avoiding events where food is the main subject (Dinners, parties, ect,), watch for binges and then super restrictive behavior.
How to seek help: Try to sit down and ask them about it, this might not go the best as people with ED's are very good at hiding it. If unable to talk to them, go to an adult THEY trust.
Most Difficult: Well firstly, its incredibly hard to go behind a good friends back to seek help for them, and secondly most people have a stigma that ED's only occur in super skinny people. However, this is not the case at all, eating disorders have no size, shape, or race.
I hope this can help! :)