I agree with GuideDogSaint. #2 is more common. #1 is understandable, but less common. There is a small difference in meaning. #1 = In this case, the word "Finding" assumes that the blood donor exists. #2 = In this case, the word "Looking" expresses that this is a search, and it is possible that they might not find a blood donor. And if the donor is already located, then you could say "The blood donor has been found." Good luck

The second one is better, although in this case (thanks to the verb aspect), it’s not a big deal. Most of the time, “to look for” is just 尋找, while “to find” is 找到.

The second one is better because they probably still want to find someone. In the first case you might say ‘… doctors have found a blood donor…’