If a girl says something about her or someone's boyfriend she may call him 'мой молодой человек' / 'чей-то молодой человек', also she may refer to him 'мой парень'.
If a boy says something about his or someone's girlfriend he may call her 'моя девушка' / 'чья-то девушка'. (Some boys refer to their girlfriends as чикса, чувиха, тёлка, etc. but these terms could raise objections from their girlfriends themselves. Smile )
BUT!
If you see a young man walking down the street and you want to ask what time is it, you may stop him with an adress 'Молодой человек, не подскажете, который час?'. In this case 'молодой человек' is not a boyfriend, but just a young man.
In case you see a girl/woman walking down the streen you may address her like this: 'Девушка, вы не знаете как попасть в библиотеку' - it's just a girl/woman in this case, not a girlfriend and it's a normal form of address.
If you have a friend you meet to drink beer in a local pub you call him just 'друг' (a friend) / 'товарищ' (a comrade) / 'приятель' (a fellow) or colloquially 'дружбан' (a buddy) / 'кореш' (a mate).
If you're a girl and you have a friend (also a girl) you go shopping with, you refer to her as 'подруга' / 'подружка' / 'приятельница' / 'знакомая'