It really depends on your individual relationships with people. A lot of women wait till after the first trimester (week 13) because the risk of miscarriage goes down significantly and they don't want to tell a lot of people and then have to tell them about the MC. Others tell right away because they feel like if something were to happen they'd want their closest family/friends to support them. I'm in the second camp and a few of my closest friends already know (9 weeks). So really up to you and whatever you feel comfortable.
There is no "safe" week. Typically people say wait until end of first trimester because the risk of MC drastically lowers but there is always a chance for complications even after that time frame. It's really whatever you are most comfortable with. We already told family and a few friends and I'm only six weeks (we told them as soon as we found out two weeks ago). We figured we wanted to celebrate with people and also have a support system should something go wrong.
It is your preference, as stated above. DH wants to wait until 12 weeks. Last time, we told his sister and our moms either the same day or the day after we got a BFP. My sister didn't find out until 12 weeks last time because we couldn't trust her to not tell anyone. I may want to tell people after the first OB appt/US. Not sure yet.
I had a chemical pregnancy in December and my family was so supportive. Even though it was a tough time, I knew that I would want their support if something happened again. Only parents, some siblings and my best friend know. I am 8 weeks today.