There is always a risk that information being disclosed, will be used in an unintended way as soon as it is shared with others however, by the time you start sharing your IP and ideas with the outside world you should have taken the possible steps to protect it.

These are different for each idea and project but of course, the most obvious one is patenting, copyrighting or trade marking the idea. This will allow you to have third party confirmation that you “own” the rights to this innovative idea and defend yourself against a newly inspired would-be competitor.
There are also ways to compartmentalize what you share with people so you are not sharing everything at once with all potential business partners. This will allow you to get people engaged without giving away the secret recipe at the first meeting. A unique idea can always be presented at a high level without disclosing the inner workings of the processes behind it.

Most importantly having confidence in the fact that you and your team is the best people to bring this idea to life will help in any interaction you have with potential partners. If you approach people with doubts in your head that this idea can easily be stolen (asking for NDAs, being all secretive, etc.), you are going to going to have a different conversation than if you approached them with confidence that even if you share your idea, you are the best person to develop it.

So in a quick summary, protect the IP, share the high-level summary first and make sure that the best person to execute it is you/your team.

I have launched several app projects in the past and went through what you describe in your question: redefining the primary audience/customer base, a couple of times.

If you have already exhausted the tools and budget available to you to reach out to your first primary target, it may be time.

However since you mentioned "a lot of advertising and reaching out", it may be beneficial to better understand what has been done on what budget so there are learning opportunities for your next campaign.

The points to consider:
• What was your budget?
• Was it effectively used/sufficient to reach your targeted audience?
• What kind of advertising and reaching out did you do?
• Are there other ways that you did not try/were not aware of?
• What percentage of your targeted audience did you actually reach?

Reflecting on what was done will allow you to better craft your next marketing/advertising strategy for the industry you target next (i.e. construction industry). You would be building on the previous strategy as opposed to starting from scratch.

If you have any follow up questions, please feel free to reach out to me. Good luck!