Assuming the boat is "abandoned" in "international waters".... I'd be in contact with the US Navy (if it were close) to ask them to check things out (or Coast Guard if close enough to US waters).
I have to ask... if someone asks for help and you "toss them a
line" - how does one figure it's now your salvage, your boat, you are owed something?
Seems to me that good practice is to assist people, period.