The following are excellent sites to use to look for an internship:
Below is the job listing for the American Institute of Graphic Arts, the AIGA, one of the oldest professional design associations in the country and their New York Chapter is very strong.You do have to be a member to see the complete job listing but a student membership is a good investment just before graduating. If you can’t afford the membership, email me and I can look up a spot for you. Also, you can sometimes find the job on the company’s site that is seeking the intern.
Other Sites that are design-centric and that will have design internships posted are:
Authentic Jobs–focuses on web design and UX/UI
Media bistro is a good site for media related job postings.