Bergvall is set to mark his 18th birthday on Friday by signing a five-year deal with Spurs before linking up with Postecoglou's first team from the start of pre-season in July.
Spurs also landed Radu Dragusin, 21, over Bayern Munich in January, and in the past 18 months have signed Alejo Veliz (20), Pape Sarr and Destiny Udogie (both 21) and Micky van de Ven, 22.
Asked how Spurs have persuaded Europe's best youngsters to join the club, Postecoglou said: "I don't think it's so much what we're saying, it's more what people are seeing. That's the important thing.
"It's like anything in life, you can try to sell a vision of something to someone but if there's tangible physical evidence of it [it's easier]. Anyone who has watched us since I've joined will have seen the aspirations we have to be the kind of team we want to be.
"That's not just me saying it, we're actually doing it. OK, we're not the finished product by any stretch but we're giving young players an opportunity: Destiny, Pape and Micky [are] all guys in their early 20s who have already played significant roles.
"So we're building a team. From our perspective it's pleasing and hopefully we become a club which is a preferred destination for talented young players.
"I've said the other day, there aren't too many hidden gems around. Everyone knows who the talents are. Hopefully our point of difference.. I've always felt your football is your biggest selling point beyond anything else. Hopefully we're showing evidence of that which is helping us."
Spurs also have some exciting prospects coming through their academy, including Alfie Devine, Alfie Dorrington, Jamie Donley, Mikey Moore and Will Lankshear.
Donley has made his senior debut this season but Postecoglou does not believe Spurs' academy is producing players at the same rate as rival clubs and wants to see an improvement.
"I think we've got a lot of work to do in our academy and [academy director] Simon Davies is certainly one that is putting a lot of emphasis and priority there," he said.
"I don't think we have the production line other top clubs have, certainly not. Even currently that’s why we’re investing in some younger players, even for the first team. For us as a football club that's definitely the way forward.
"My brief at the moment is still very much around the first team and building a first team and you can do that while giving opportunities to young players. If anything I think for sustainable success it's the best way to go because the team grows together when it's guys of similar ages as long as you've got good experience around them.
"That's what we're doing at first-team level. We've still got a lot of work to do at academy level. We've got a great man there in Simon who has worked at some of best academies going and he knows what’s needed. We've got some good coaches in there now.
"This year has been better but in terms of a production line of young players I think we’re still well behind other clubs.
"If young players don't feel there is an opportunity here maybe we don't get the best ones or maybe we don't provide the opportunities for the best ones, so my role in that is to make sure the good ones we have do get an opportunity.
"And secondly, other young good young players around the country, not just around the world, see this as a club where if you are talented, you will get an opportunity."
Spurs visit Everton in Saturday's early kick-off, with Postecoglou to welcome back Sarr after Senegal's elimination from the African Cup of Nations.
Captain Heung-min Son remains away at the Asian Cup, with his South Korea side due to face Postecoglou's native Australia in Friday's quarter-final.
"It's kind of a win-win for me," the Spurs manager said. "Obviously being Australian I'd love for them to get through then we'd get Sonny back.
"But part of me would love Sonny to win an Asian Cup. I know what it'd mean to him and his country.
"They put great stock in that competition. And Sonny, for everything he's done for the game and his nation, as disappointed as I would be if Australia go out, I'd love Sonny to go all the way and don't mind if he missed a couple more games for us."