Investors don't seem to have much confidence in Walgreens Boots Alliance, and the drugstore chain hasn’t said much to ease their concerns.

Walgreens is testing new concepts, including adding optical and vision services to some stores. It’s also partnering with health-care companies, such as insurer Humana to open two senior-centric stores and LabCorp to offer lab testing in a handful of stores.

It hasn't outlined its grand vision, though, to the frustration of some investors.

Walgreens' traditional rivals are trying to sell investors on their futures as they pursue massive deals. CVS Health is acquiring health insurer Aetna for $69 billion in a deal it says will transform it from a company that fills and manages prescriptions to one that can serve a broader range of consumers’ health needs. Grocery chain Albertsons is buying Rite Aid in a deal the two are hoping will combine its grocery business with Rite Aid's pharmacies.

But perhaps Walgreens' biggest rival yet is just entering the space. E-commerce giant Amazon is buying online pharmacy PillPack, a move that could reshape the prescription drug delivery industry. The mere threat of Amazon has hung over Walgreens, CVS and Rite Aid's stocks, as investors fear the e-commerce giant will crush retail pharmacies the same way it has bookstores and toy stores.

Its acquisition of PillPack on Thursday rattled them even more. Walgreens shares tumbled 9 percent, CVS' slid 6 percent and Rite Aid's lost 11 percent. The three lost $11 billion in market value Thursday alone.

Walgreens lost $6.3 billion in value, bringing its market capitalization to $59.51 billion.

News of the deal broke Thursday during an earnings call between Walgreens executives and Wall Street analysts. CEO Stefano Pessina told them he's "not particularly worried." He said that doesn't mean Walgreens isn't complacent, but it also doesn't mean the company's going to go out and buy something in response.

"I have always said that we have to separate the emotions from the facts," he said. "We don't see any reason to be worried. We are not complacent. I repeat this. We have a clear plan. And I believe that we will continue with the execution of our plan."

Yet Walgreens hasn't given investors much insight into the plan. Pessina deflected questions about it last month at the company's analyst day. He said Walgreens has a strategy — he just can’t say what it is.

“The only thing that I can tell you is that we understand the world around us,” he said. “We understand the changes that the world is going through, and we will adapt our business to follow it. I wouldn’t say it if I have not, if we have not a clear strategy in mind. We are testing. You can see some of our tests. You don’t see what we are doing behind the scenes. The only thing I can tell you is that we work for it, and at the right time, we will see whether or strategy will work or not.”

Even without the Amazon announcement, investors were concerned about Walgreens' third-quarter results, including soft same-store sales numbers, particularly at the front of the store, where the drugstore sells greeting cards, household items and personal care products.

Management not wanting to talk about its strategy is frustrating investors, said Jefferies analyst Brian Tanquilut.

J.P. Morgan analyst Lisa Gill said Walgreens’ management isn’t communicating its strategy as best it could, and investors want to see results.

However, she said these things take time and it’ll take about five years to see whether CVS or Walgreens’ approach is better. CVS is betting its future on a large deal, while Walgreens is sampling different partnerships.

“Even people who claim to be long-term investors need short-term results,” she said. “They want to put their investment thesis on, and it’s just not enough for people. So I think that’s why people keep asking, asking, asking.”

With Amazon entering the space, the questions aren't likely to end anytime soon.