Regex for matching HashTags in any language

I have a field in my application where users can enter a hashtag. I want to validate their entry and make sure they enter what would be a proper HashTag. It can be in any language and it should NOT precede with the # sign. I am writing in JavaScript. So the following are GOOD examples: Abcde45454_fgfgfg (good because: only letters, numbers and _) 2014_is-the-year (good because: only letters, numbers, _ and -) בר_רפ×לי (good because: only letters and _) арбуз (good because: only letters) And the following are BAD examples: Dan Brown (Bad because has a space) OMG!!!!! (Bad