Realize that any decent web designer gets asked constantly to build or design something "for their portfolio" or "for experience". This is a huge, waving, flapping, red flag to designers. Or a neon sign which simply blinks "WORK FOR FREE."
Any designer worth their weight, doesn't need your project for a portfolio piece or experience. Generally because a good designer already has a strong portfolio or is perfectly capable of creating portfolio sites without completing your work for free.
If you are interested in a partnership, then you need to approach the offer as a partner offer. You need to treat any designer as though they are an investor in your idea because, well, that's what they are. You need an elevator pitch, a business plan, what value added items the designer will acquire from the work, etc.
No-Spec.com has a few article warning designers as to why work such as this is just a bad idea. If your needs fall within those parameters, you may have a very hard time finding anyone.
Your best bet is to find other recent or soon to be graduates from your school.