you may well have tried this already, and I know it may sound lame - asking an attractive girl for directions, make sure its on your route, excuse me, smile, eye contact, I'm looking for (destination of your choice) thank her genuinely and be on your way
Try this for a week or two
It purely gets you into the mindset of stopping women on the street that you like the look of. Its also low risk / low investment - MOST girls are socially adjusted and will help you if they know, even those with earphones in (sod's law the first one will be a foreign tourist
). Avoid any temptation to turn it into an approach at all costs - as this will place you in the manipulative/deceitful/lame category.
"say hi? then what" if you say hi, she will say hi back and just walk on - just like a girl would ignore a hi in a dating message, there is no hook, people say hi all the time, its just noise... whatever words emerge from your mouth they must be delivered in calmly, slowly, with good positive vibes and accompanied with friendly eye contact. Tell exactly why you noticed her
"what do i talk a bout" anything interesting/non-freaky, tell her about your plans for the day, find out hers - avoid / steer conversation away from work, women find talking about their jobs dull as hell - even if you find the idea of them being a stripper fascinating
If you get past this stage and feel you've been talking for more than a few minutes, it's a safe bet she's interested in finding out more, so invite her to go for coffee there and then, or if not feasible for you or her - the number close. Email/Facebook are a waste of time.
"should i stop her in the middle of the street" yes - much better than at the end of a dark alley
"there is too many people around" exactly, so who will notice? and if she is that insecure about a bunch of people seeing you chat to her on a busy street do you want to date her anyway?
"i wanna talk to her but she's on the phone" yeah, probably best leave these alone - she is already engrossed elsewhere, you will definitely be seen as an annoyance
"she's with people" stick to single girls at first, or maybe twos if they are giving you the vibe - talk to both initially, then focus on your target
if you approach you will immediately stand out from the rest of the dorks who stand/stare/wolf whistle/shout "hey gorgeous"/follow her/walk close without speaking
avoid groups of girls with guys in them - even if they are just their friends
avoid girls who are talking to themselves - no matter how hot they are
avoid girls who are speed-walking while shouting "my boss is an asshole!"
when approaching, keep outside their intimate zone - an arms length
the easiest ones are the one's who give you the eye glance / smile / hair flick or combination of all the above as you walk nearby