They are spending £125 for blocks of 1,000 friends on Facebook and Twitter.
The virtual friends are being sold by a small Australian company called uSocial.
Leon Hill, its 24-year-old chief executive, reported a surge of inquiries about his service over Christmas.
He told The Sun: "Social networking sites can be cruel if you're unloved – they show exactly how popular you are.
"People are buying pals so they have more mates to chat to, rather than sitting alone on their PCs."
However, many claim the service abuses the principles of social networking sites.
One objector, who set up a website leanbhill.com, wrote: "uSocial utilises armies of dummy accounts on social networking websites to cheat and promote content on behalf of its clients.
"In other words, uSocial violates online communities for money. This is shameful and deplorable.
"It exploits the assumption of trust and goodwill that allows internet communities to thrive."
Lawyers for Facebook have also tried to get the service shut down.