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Hey! You have to use Bittrex.

Here's a helpful guide I used earlier today!

https://chaseohlson.com/how-to-buy-antshares/

Let me know if you have any questions, but it's really straightforward.

As a matter of interest, why are you looking to invest?

Many exchanges, including Bitrex.
You can always find out the exchanges that sell a certain coin by using coinmarketcap, select the coin and click Market.. for NEO (ANS) https://coinmarketcap.com/currencies/neo/#markets