Google translate shows "What's new?" as 新着情報？ Is it a commonly used expression?
A literal translation of 新着情報 is latest arrival of information, used on webpages, programs and newsletters. http://jisho.org/search/%E6%96%B0%E7%9D%80
For casual conversation, there doesn't seem to be a one-size-fits-all translation. Here are some suggestions:
My ex-girlfriend (Japanese) taught me the following casual expressions.
最近どう？ (How have you been recently?)
良さそうじゃん。(You seem well)
調子どう？ (How are you? Literally: How is your condition?) Though, it might be taken as an enquiry of the listener's health
Weblio has a few more ideas:
変わりはないかい。(Literally: Nothing changed recently?)
何か変わりはない？ (Literally: Anything different?)
何か変わったことは？ (Pretty much same as above)
やあ、調子はどう。(Literally: Hey! How are you?/How is your condition?)
There are other more specific expressions, for instance, how is your business going? and so forth. They depend on the context.
However, it doesn't seem you can use an exactly equivalent expression in Japanese - i.e. 'Hey! Great to see you. What's new?' As an illustration of this point, I sat in an English class where the lecturer (who was Japanese) had everyone stand in a circle and pass around a ball. The person throwing it said, 'Tell me something new and exciting that has happened to you recently'. The person receiving the ball usually had to pause a long time and eventually gave an awkward answer. In my English classes, I generally had to give a lot of encouragement to get my students to answer a similar question. Answering it didn't seem to come to them naturally.
More specific questions, however, seem to elicit a prompter response without the awkwardness.
You could say:
元気？ (Are you well?)
今日何してたの？ (What were you doing today?)
お疲れ！ (Literally a compliment on their hard work that day. Can roughly be translated as: Hey! Nice job today. You've earned a rest!)
You have to be careful about not being too casual with strangers and older people etc.
Edit: The difficulty with 'What's new?' is it bundles a greeting and an enquiry of news/gossip from the listener. There's no catch-phrase which has the equivalent value in Japanese. If you want to convey something similar, you have to go with whatever expression is appropriate for the occasion, which takes a lot of practice. The same difficulty exists with 'Have a nice day!'. The translation of いい一日を doesn't really work. You would have to use a native expression that doesn't exactly convey the same feeling and is adapted for the situation.