I did. He and my mother had a one night stand when she was 18 years old. He knew she got pregnant,and offered to pay for an abortion. When she refused that option, he denied he was the father. She was always honest about it, and even told me his name. When I was eighteen, I tracked him down and sent him a letter. At first, he didn’t want to meet me, but I insisted. I told him if he didn’t meet me voluntarily, I’d show up at his front door. I didn’t want anything from him, just background information and such. We met for lunch, and 4 hours later we were both crying, happily. The next week, his wife invited me to their home for dinner, where I met my half-brother. We all became friends, if not exactly family. He got to hold his first grandchild (my first daughter) before he died at 52 years of age. I have never regretted taking the steps to find him. Now, your situation sounds a little different. If he was an anonymous sperm donor, he may well not feel the same way as my father (eventually) did about being found. Also, my father told me that if I’d contacted him 5 years earlier, he would have told me to fuck off. He had changed a lot by the time I found him. Tread carefully, and protect your heart.