My DS (just turned 15) was donor conceived, in the UK, so will be able to contact his donor when 18.
I would best characterise him as being completely uninterested! We made it part of his story from babyhood (through books from Donor Conception Network, and also attending Donor Conception Network events). He has a vague curiosity about the potential for meeting his siblings, thinks that will be cool, and when I ask if he will meet his sperm donor he says 'yeah, might do one day'. But it's SO not an issue, or part of his identity. We're fortunate that he's very chilled, very secure, very stable (might have to thank the donor for that!) and I'm aware that things might change at different stages of his life, but I honestly do not think its had, or will have, a negative impact for him.
We've stopped with the Donor Conception meetings when he was about 10 as his genetic origins are so not a big deal for him that we were scared that banging on about it might make him think it should be! (We would of course revisit if he expressed an interest, or started to struggle with it). We actually have a pen-sketch and goodwill letter from his donor which we have asked him if he wants to read but he's never got around to it! But it's not a topic of conversation he/we avoid - he might randomly say 'learnt about eye colour in biology today, worked out my donor must have had blue eyes' or I might say 'that's funny you are so anti-smoking, cause your donor mentioned he was too in his letter'. So it's part of his life, but a very very small part.
I've just asked him how often he thinks about being donor conceived and what he thinks about it. His replies (verbatim) were "Once every 4 months" "It doesn't really affect me". And then he went back to his gaming.
So no teenage angst here!