Is Twitter used even to say the first hello or is email still a better way to approach someone?
A very good and valid question (particularly in this age of instant and social media). I personally prefer e-mail, but I'm fairly "old school" like that. A few of the ladies I know will interact almost exclusively through Twitter and/or respond to Twitter direct messages quickly or more quickly than e-mail. For example, a lot of our recent coordinating with Shauna Ryanne was done through Twitter, though, granted, we had a pre-existing work rapport.
I've never reached out to anyone using only Twitter as a first contact to directly hire him/her. But my first recent social interactions with Minxy Li were through Twitter alone. So, that is sort of a first contact. She's also an avid Twitterer.
So, whereas I *personally* would go the e-mail route, someone who uses Twitter a lot might not bat an eyelash at a Twitter first-contact. And, of course, you might sometimes find that a e-mail might not get you a response, but Twitter direct message or @ tweet might be the thing to get the response.