If I had a dollar for every-time a potential client thought their app was so cool that I should be begging to work on it just to get a portfolio piece, well, I would have quite a few dollars.
To be quite honest I would look at some half implemented Reddit mock-up as a half implemented amateur example of someones work. I want to see fully working apps that a developer can explain to me what portions they built and why features where built.
To be honest I would be embarrassed to use a few hour throw together as an example of my work. When I have far better examples of applications that are professional and complete.
My intent is not to be arrogant about the matter but the reality is there are very few professions where asking someone to work for free to get a portfolio piece would be met with a straight face.
Lawyers do pro-bono to help the downtrodden doctors do research work to advance the state of the art but nether do routine work to get a portfolio piece. So unless you are asking someone to do state of the art groundbreaking research work or it is charity (open source) to ask someone to do it for portfolio work is akin to asking a lawyer to take your DUI case or a doctor to fix your problem to get some portfolio work.
