If the social enterprise that I was starting was for a specific cause, I would get to know people who believe in the same cause and from them look for potential funders and talents. I would also try to find out which corporates have that cause for their CSR (corporate social responsibility) and try to talk to them as potential funder. But at the same time, I would try to bootstrap the business and try to get it funded by the customers that I was targeting. Some times too much money may not be a good thing. You may lose focus and start doing the wrong things.

Simple answer. Non-profit doesn't aim to make any money, they usually are started for a cause and live on donations. Because of that, they may be regulated under charity and have different requirements in some countries. Think NGOs and some charities in your area. Social enterprise on the other hand, can also be started for a cause, run like a "normal" business, using business models and strategies to get to financial or operational sustainability. Typically, their primary goal is to make a difference in their cause, thus creating a positive impact to the society. They aim to make profit so as to achieve sustainability, but the goal of social impact is higher ranked than profit. In my humble opinion, all enterprises should be social because all of us should aim to create positive impact to the society.

Are you thinking about a website? Or a web-application? There are plenty of web development companies (from low cost to great team and reputation) out there which you can share your requirement to them and get a quote. If you are just building a prototype to test your idea, you can even get freelance developers and designers to do it. Go to some known hubs where developers and designers are known to gather in your area and start talking to people.