This is not the appropriate way to use a donor and puts both you and your potential child at risk, as well as the donor!
There are so many issues.....
The high risk of sexual disease
The risks of inherited problems
Lack of legal clarity
Lack of counselling and understanding of the implications on both sides
The high potential for your child to have an unlimited number of siblings - how will this impact your child?
The emotional impact on your child - how are you going to explain to them that they were conceived this way? How will that impact their self worth, relationships, etc?
Why is the donor doing this? It won’t just be to help people - if this was the case they would use a reputable clinic
Etc etc etc
I am assuming with all of this that you wouldn’t meet them on Facebook and then go down the proper route, so apologises if I’ve got that wrong!
Why would you not use a registered clinic and donor?