Immigration Law Questions? Ask an Immigration Lawyer.
What is happening really depends on the facts associated with your friend's situation. It is possible that the $5k is for bond/bail and that he will have to attend a hearing in the future to determine his rights in the country. To the extent that he does not have a legal basis for entering or remaining in the country, it is possible that at that time he could face deportation.
If I put the money up... Am I tied to him?
Say if they give him a court date and he misses it, will they come after me?
The bond would be forfeited. They would not likely come after you, for purposes of punishing you. However people may show up on your doorstep looking for him if they know about your friendship.