This is an interesting question. The worth of something is determined by demand. Right now, many cryptocurrencies are very in demand and can even be used to buy things online or in traditional stores. Cryptocurrencies also trade in exchanges that do assign a value to the currencies, and you can buy and sell them like you would stocks, which gives them value. Keep in mind though that there are reportedly over 900 types of cryptocurrency available right now, and not all of them are in demand or worth anything. There is also some debate on whether cryptocurrencies will be worth anything in the future.