I think Katy's answer is unfortunately quite misleading. "Kevin contributed a lot on the pitch presentation yesterday" is grammatically correct, however here she has used "contributed" on its own, it is not connected to the "on", which belongs together with "on the pitch presentation".
As Neil pointed out, "contribute to" is correct, because the idea is that you contribute towards something. This "towards" is then shortened to simply "to". "Contribute on" is grammatically incorrect.
Here are some more examples with "contribute" and "contribute to":
- What is he contributing to the project?
- You should donate some money to help contribute towards cancer research.
- During the job interview, the he asked me: "What can you contribute to the company?".