Depends on severity. Most teens go through periods where they hate their body either realistically (severe acne) or not (unfamiliar body changes). Calm assurance that the body is still changing helps many. For real issues, seeking medical attention, like a dermatologist for acne, can be of great value. If the self-perception is truly unreasonable and impairing, the psychological or psychiatric help may be needed.
Body image. Support from family, friends & your therapist are vital.
Possibly. This depends on whether your friends are truly friendly, as I hope yours are. Such friends can be a great support (more than strangers) because they love you for yourself, and not your physical appearance. If they listen and care about you, they'll gently let you know when you're over-emphasizing a perceived bodily imperfection & need to be more accepting of yourself -- & need to get help too.
Talking. It sounds like you may have concerns about your teen. I would encourage you to talk to your teen in a variety of different settings to help see if this is one of their concerns. Sometimes parents can ask their teens if they know any of their friends experience such issues. Utilizing movies that display the behaviors may also be an effective way to talk and listen to your teen.
No. A disturbed view of one's body weight or shape is one symptom of an eating disorder. But, some people have distorted body images and do not meet criteria for an eating disorder.
No. An eating disorder requires behavioral action on that thought.