I live in Denver, CO and 11 months ago my brother moved to Denver supposedly to take a job here and came to stay at my house as a guest since it was near the holidays and his job was not going to start until after the first of the year. He has remained at my house now for a 11 months and never paid any rent, never paid any utilities or paid for any groceries. The job fell through and it was not until about a month ago that he finally found a job. I have told him that he needs to be out by December 1st but he does not seem to be moving forward with finding a place to live.

What rights do I have? Do I have to formally evict him?

Do I have to formally evict him?

See the discussion (in the next paragraph) of whether the landlord-tenant laws apply in this situation. Assuming they do, you should give him written notice that you want him out. Without looking up how much time you need to give him in Colorado, it is generally 30 days. If that is the time in Colorado you would have to give him until at least December 5 (assuming you give him the written notice today).

It is open to dispute whether he is a "tenant" according to the landlord-tenant laws. This question will depend on the statute and case laws in your state. But if he is considered a "tenant", you would probably be prohibited from constructively evicting (or "ousting") him by doing such things as changing the locks, turning of the heat and utilities, etc. You would have to take him to court if he won't leave on his own.

First, put it in writing that he must be out by December 1. I beleive in CO the minimum amount of time you must give for eviction where there is no written rental agreement is 10 days, so if you're willing to put up with him until Dec 1 that meets the minimum notivce requirement. It must be in writing - merely telling him verbally that he must be out doesn't count. If he doesn't go by then , then yes - you will have to formally evict him.

... I beleive in CO the minimum amount of time you must give for eviction where there is no written rental agreement is 10 days, ...

This (http://www.landlordguidance.com/eviction-notice-forms/colorado-eviction/) link suggests that you are correct.

And yes, it has to be a formal eviction process if he will not just leave, after you given him a written notice to move.