We find a lot of the time, when we are asked to come in to look at a search that has been out there for 6 months, we noticed the only pool targeted are the active applicants and some referrals.
In the tech space, understanding your technology space landscape will tell you otherwise. If you take the time to map out your competition and technology network, it is nearly impossible to saturate your talent pool. Not to mention if you create a talent pipeline instead of a pool, but that is for another topic.
Mapping out your talent pool avenues may sound daunting, but that's why many people don't do it, no time, don't know how perhaps. But it is essentially understanding the technological landscape of a particular space first. You need to create a map of where you can search - the most obvious one is to look at your competitors; although most competitors have competition clauses, you need to be wary about those things, but more often than not, there are always workarounds.
Next are the adjacent technologies - or companies whose products work well with yours, for example - network and security, another is backup and storage. These avenues are a great pool of potential candidates, especially if you search for non-technical roles like sales and marketing. Technical roles can be a little trickier, but if you leave room for some learning curves, you should be able to use your adjacent technology mapping just as well.
Also, reaching your target audience via what we call a 360 network. No man is an island; the same can be said with every role. Whatever role you are sourcing for, that role is working with multiple people of different roles - define that network, and you can start building your sourcing avenues. For example - every sales representative in the tech industry works with presales, partner managers, technical consultants, and even project managers. They can be your sourcing avenues. Check your network for these people, and start working on your referrals.
Once you have mapped all these out, your sourcing will be more strategic and targeted.