I'm a little bit late to this. I would really recommend what @Stroopwaffels said above.
Although I haven't met any people through Ancestry, 23andme etc who were adopted, I have come into contact with a couple of the children of adoptees (is that the right word?).
In the first case I found, through a DNA test (it was actually on 23andme rather than Ancestry, but I've done tests on both sites), that I was related to an American woman on her father's side of the family. Her father knew that his mother had been adopted while living in England but that is all. The adopted child later married a US serviceman and emigrated to the USA.
After we worked out how closely we were related, combined with what little information they had about his mother, I was able to identify who she was (it turned out that his mother (the adopted child) and my mother were cousins) and gave him a whole load of information about his family that he had no idea about.
It absolutely blew him away. He had resigned himself to never really knowing anything about his mother's birth family (she died quite young) and was overwhelmed that just from his daughter doing a DNA test he was able to find out about his real family.
In the second example, a DNA test showed that I am related to a woman living in London whose mother and aunt had both been adopted. It has been an interesting story to unravel.
She was keen to find out who her mother's birth parents (her grandparents) were.
It turns out that the grandmother was born in County Galway, Ireland and then married while she was living in Wexford.
Her husband was a policeman who had recently returned from China where he had served for six years in the Shanghai Municipal Police (many Shanghai policemen at this time were Irish or British).
However, it appears that life in County Wexford might have been a little too quiet for him as the following year he joined the British East African Mounted Police based in Nairobi, in what is now Kenya, and her grandmother went with him.
Unfortunately he died two years later and her grandmother returned to the UK.
About five years after his death, her grandmother gave birth to two daughters (my relative’s mother and aunt) and they were both adopted at an early age.
Normally, if a woman was unmarried then no father would be shown on the birth certificate. But in both cases her widowed grandmother gave the name of her deceased husband as the father. In reality, given the DNA test, it appears that it is some relation of mine that was the father.
They were fostered for a while in another part of the country before being adopted and returning to London.
So, we have been able to trace a lot of the story of her mother’s birth family although I’m still working on exactly which relative of mine might have been her grandfather.
Just a couple of random stories about my experiences on Ancestry and the other sites like 23andme and MyHeritage