Roll20 have several Looking For Group (LFG) options to find people to play with.

1. The Looking For Group Tool tool built into Roll20. Games that starts soon called Pick-up Games can be found here.

2. The Looking For Group Roll20 Subforum - The FLG section of the official Roll20 forums

3. Try finding games outside Roll20's official channels. The r/Roll20 subreddit have a short LFG Guide with some community options.