We just open sourced a easy to use library called Magnitude that handles out-of-vocabulary words and uses Annoy indexing for fast most_similar queries for word2vec, GloVE, and fastText:

https://github.com/plasticityai/magnitude

Just an FYI, FastText's default implementation handles OOV words via word n-grams and character n-grams. (see switches -minn, -maxn, and -wordNgram)

https://fasttext.cc/docs/en/options.html