When a parent abandons their kids, their title as parent isn't automatically stripped away. They may be physically and psychologically distanced, but their adult kids fully have rights to track them down and address the years of abandonment, and how it affected them.
Unfortunately, the real issue here isn't whether adult kids have a right to track down their absent parents, but rather, whether it'll ultimately do more emotional harm than good.
In a recent post on the Am I The A*shole subreddit, a woman asked if she was wrong for tracking down her mom and telling her mom's current husband about the kids she left behind.
AITA for telling my mom’s new husband that she has kids?
OP's mom left her and her brothers when she was 15, and from then on OP was raised by her dad and uncle.