Although you still are under the age of majority at the age of 17, and cannot make any decisions for yourself just yet, unless you have been emancipated (which I do not think they do in Michigan anymore), the police may try and hunt you down at the direction of your legal guardians. However, without that push I do not think they will do much.
However, a minor under 17 can contract for his necessities, ie for an apartment and things of that sort, so he can technically make it in the world.
There is no such act as "legally running away." The 17 year old is still a minor and responsibility for the child's actions may fall on the parent(s). However, there truly is no place for a 17 year old in the juvenile system, such as a youth home, and this is not the type of matter which would be pursued by the police. As the saying goes, the police have "bigger fish to fry" than a runaway who is 17. I don't know if this is the 17 year old or the parent asking this question, nor do I know when the child will reach 18 years of age. Nevertheless, the 17 year old could file for emancipation, but by the time all is said and done, the 18th birthday might be just around the corner. The link I'm posting relates to procedures for emancipation:
Neil M. Colman
Mr. Colman is licensed to practice law in Michigan. The response herein is not legal advice and does not create an attorney/client relationship. The response is in the form of legal education and is intended to provide general information about the matter within the question. Oftentimes the question does not include significant and important facts and timelines that, if known, could significantly change the reply and make it unsuitable. Mr. Colman strongly advises the questioner to confer with an attorney in your state in order to ensure proper advice is received.