No, I don't think it is really. That's my first thought anyway. I guess my daughters friend is the hugging type and does it to me every time she sees us but it makes me a bit uncomfortable. I definitely would not allow it if I found myself alone in a room with her ( something else I would not let happen) but this girls parents are the same way so I figure it's ok. Under normal circumstances I just don't think it is appropriate. I would rather be safe than be accused of something.
A man can hug a teenage girl that he is not related to. However, this will depend on which grounds do such an act happens. If there is an achievement may be in school work or in any other task a man can hug the girl as sign of appreciations. If there is no any kind of achievement, then one should question the reason behind such an act.