Yes, you can use paid ads, Facebook, Google etc., but it won't get you far if you don't have $100k+ funding.

What you need is something that gives you 100,000 users while spending $0. This is the task of a founder, and it's difficult. Possibilities are Guerilla Marketing, PR-Stunt, Partnerships with bigger brands and a lot more. Let me know if you want to find an idea.