Can you sue a person who has no money?

You can sue anyone, whether they have money or not does not matter. What is likely to happen is that they will not have money for a lawyer and will not contest the suit. The court will issue a default judgment in your favor.

Then you can try to collect on the amount. If they have no assets, there isn't likely to be much success in collecting. However, it is possible to get a seizure order or a garnishment to take their personal property and sell it at auction to satisfy the debt, or garnish their wages to collect the amount due.