They usually provide a TX ID in your withdrawal history. Did they? If not, what does your history say? If you have a TX ID, and feel comfortable posting it, please post it here.

If the withdrawal really is stuck: Make a post on Reddit at r/bitcoinmarkets. Cross-post it to r/bitcoin. Tag one of their reps in the post: https://www.reddit.com/user/bfx_brandon

I would also link to the post in a tweet sent to @bitfinex on Twitter, with hashtags #bitfinex and #bitcoin. The exchanges tend to be more responsive when complaints start being circulated on social media. Sad but true.