There are a ton of services available. I use a handful described here.
The more serious (and accurate) services are usually subscription-based (eg, Transunion’s TLOxp) . Some services allow only one lookup at a time (eg, PeopleFinders). Others allow batch processing of hundreds of records at once (eg, MelissaData). Still others offer a hybrid solution (eg, Pipl.com).
Also, as a search primer, check out this article:
Couple of tips: 1) consider paying a virtual assistant from UpWork or somewhere similar to do this time-consuming task; 2) use a couple of services to triangulate and verify your results. I’ve found that each service has varying levels of data quality. Also, one service may provide you with one critical piece of data (eg, home address) while another provides an item that rounds out the profile (eg, cell phone).
If you learn of other services, I’d be interested in hearing about them as well.
-Stephen