There are many ways to reach out to others via Twitter.
As you start sharing content with certain hashtags, pay attention to those users who are using that hashtag. If they contribute frequently, chances are they're someone you might want to get to know better. So talk to them!
You can also find specific people on Twitter by using twitter directories. One of the most common isWeFollow. You can search for users by hashtag or groups, such as recruiters. This is more of a cold call approach. It's best to ease into the conversation when engaging someone. It's better if you repeat (or “retweet”) their tweets for a while or comment on articles they share before directly trying to start a conversation. It's considered more polite that way.