"Contribute for" or "Contribute to" or "Contribute on" or "Contribute in"

We said :

I do want to thank Mr. Foulen and Mr. Felten who contribute for server hosting .

or

I do want to thank Mr. Foulen and Mr. Felten who contribute to server hosting .

or

I do want to thank Mr. Foulen and Mr. Felten who contribute on server hosting .

or

I do want to thank Mr. Foulen and Mr. Felten who contribute in server hosting .

Solution 1:

I do want to thank Mr. Foulen and Mr. Felten who contribute server hosting.

The server hosting is what Messrs Foulen and Felten contribute, so there is no preposition; it is the object of the verb.

In doing so, they are contributing to the project, and also contributing to the beneficiaries.

Unless they were offering an opinion, in which case they did indeed contribute on server hosting, though it would be clearer as "who contribute on the topic of server hosting".

Quite likely all of this would be better in the simple past (contributed rather than contribute) even if their contribution is ongoing.