If you sold bitcoins in 2017 for a gain – you will need to report the gains and losses related to the transactions if they were held for investment (similar to stock transactions). If you have accepted bitcoins as payment for goods or services in your business, you mush include the value in US dollars of the bitcoin transaction in your business income. For US employers who pay their employees in bitcoins, they need to report the US dollar value of the bitcoins paid on Form W-2.
The IRS is pursuing the means to obtain names and records of US customers who have bought and sold bitcoins through various virtual currency exchanges. Using bitcoins to evade taxes is illegal.