Ahoj, jak vhodně přeložit něco takového: “V první části musí vyřešit záhadu zmizelé mladé dívky, která byla viděna naposled před 30 lety a její strýc se jí snaží stále najít.”

“In the first part, they have to solve a mystery of a missed young girl, who was seen last time 30 years ago and her uncle has been trying to find her.”

Ještě mě napadla verze s present perfect continuous pasive, ale tohle asi není úplně vhodný použití, předpokládám. “In the first part, they have to solve a mystery of a missed young girl, who hasn't been being seen for 30 years and her uncle has been still trying to find her.”

Děkuji

they have to solve a mystery of a missing young girl, who was last seen… / who was seen 30 years ago for the last time.
Tu druhou verzi by asi nikdo moc použil, je to zbytečně složitá konstrukce.

1. Solve the mystery of (“mystery” is defined); see Ngram.
2. a missing young girl who was last seen 30 years ago and her uncle has been trying to find her.”

" … and her …" is not good stylistically here because the subject of the clause is “who” (referring to “young girl”), and then a different subject (“her uncle”) is introduced in the successive clause.

…a missing young girl who was last seen 30 years ago, (and) whose uncle has been trying to find her."

…a missing young girl who was last seen 30 years ago. Her uncle has been trying to find her (… but to no avail).

And note the important point made by DM above, no (Slavic) comma after “girl” because it introduces a defining relative clause – určující vztažnou větu, která se neodděluje čárkami (Help For English).

… who hasn't been being seen- …

Thank you both. Dan, I know that I mustn't put commas between relative clause. Unfortunately, I didn't realize it is a relative clause. I still have a lot to learn. I'm still not used word such whose, whom. And articles is problem as well. I hope it will get better.