Let's suppose I have some ammount of money in virtual wallet like Paypal or Bitcoin. Are there ever any systems or institutions which would enable one to invest virtual currency, for example, loan at interest? Is there anything like financial market of virtual currency?
I don't know much about paypal or bitcoin, but I can provide a little information on BTC(Paypal I thought was just a service for moving real currency).
BTC has an exchange, in which the price of a bitcoin goes up and down. You can invest in to it much like you would invest in the stock market. You can also invest in equipment to mine bitcoins, if you feel like that is worthwhile. It takes quite a bit of research and quite a bit of knowledge.
If you are looking to provide loans with interest, I would look into P2P lending. Depending on where you live, you can buy portions of loans, and receive monthly payments with the similiar risk that credit card companies take on(Unsecured debt that can be cleared in bankruptcy).
I've thrown a small investment into P2P lending and it has had average returns, although I don't feel like my investment strategy was optimal(took on too many high risk notes, a large portion of which defaulted). I've been doing it for about 8 months, and I've seen an APY of roughly 9%, which again I think is sub-optimal. I think with better investment strategy you could see closer to 12-15%, which could swing heavily with economic downturn. It's hard to say.