No. Just no. Sure, once you have some users (and are actually providing a useful service, or something fun, to them), you could encourage them to get other peo

No. Just no. Sure, once you have some users (and are actually providing a useful service, or something fun, to them), you could encourage them to get other people to join, perhaps via an invite link, or just a note on the main page asking them to. You could even give them benefits if they attract more users to the site (temporarily remove ads, give them some benefit, or whatever, depending on what type of site it is). But requiring users to get more users to join will drive them away, and is sort of an admission of the fact that the site isn't very good. After all, if it was, users would recommend it to their friends because they liked it, not because they had to.