Are there any extensions which allow for Prospect Management & Tracking? I came across a planned extension called "INTEGRATION WITH DONORSEARCH" but it doesn't look like it has been completed yet, though target date was February 15, 2017.
You may want to check out CiviProspect. From the README:
CiviProspect provides the core structure for creating/ managing/ converting the fundraising opportunities of an organisation. It can also be used to manage any monetary opportunities such as sales opportunities and event sponsorships.
As I understand it Donor Search just helps you find better matches, but for managing and tracking that's what CiviCRM already does. You would just use contacts and activities, and if you want something slightly more structured there is CiviCampaign.
If what you're really asking about is tools to help you find prospects in the first place, then that's a slightly different question.
I worked on the DonorSearch extension. I spoke to my sponsor last week, who said it was done except for documentation. I would go ahead and install it - I believe DonorSearch allows a free account for CiviCRM users that gives 50 searches per month.
It looks like the 1.1 branch is the most current.