The sites now have tens of thousands of members, Mr. Chaiwala said. Most registered users are in Britain or the United States, even though bigamy is a crime in both countries. But some members log in from India, Pakistan, or other countries in Asia or Africa where it can be legal.

While he has no way to know how many polygamous marriages his sites may have facilitated, Mr. Chaiwala said he had received more than 100 letters from users thanking him for guiding them toward multiple-marital bliss.

Mr. Chaiwala speaks of his sites with an evangelist’s fervor, hoping to spread the idea that polygamy offers a pro-family antidote to promiscuity, prostitution, divorce and broken homes. He dismisses those who criticize polygamy as anachronistic, saying it is better than adultery or one-night stands facilitated by apps like Tinder.

“I am saying, ‘Marry two or three, and be loyal to them,’ ” he said.

Creating a profile on either site is free, but to browse profile photos, you need to upgrade to a paid membership of $20 a month or $45 for three months.