A comment on another question compared Voldemort and sex, which made me think of Sigmund Freud and JKR. We know that V. never loved anybody, but that says nothing about his sexual experience. Were fame, power, and artifacts the only things he lusted after?
JKR knows, but she ain't sayin'.
Q: Was Voldemort a virgin?
JKR: Does a dehumanised wizard killer who murders in the pursuit of his own immortality forfeit the right to ALL privacy?
Edited for clarity
That being said, there were persistent rumours in the wizarding world that Scorpius Malfoy (Draco's son) was actually the Dark Lord's son via some time-travel nonsense.
SCORPIUS: The rumor is that my parents couldn’t have children. That my father and my grandfather were so desperate for a powerful heir, to prevent the end of the Malfoy line, that they . . . that they used a Time-Turner to send my mother back . . .
ALBUS: To send her back where?
ROSE: The rumor is that he’s Voldemort’s son, Albus.
And Delphi (Lestrange) certainly believes herself to be the product of Bellatrix and Voldemort, having been told so by Rodolphus Lestrange
DELPHI: I am from the future. The child of Bellatrix Lestrange and you. I was born in Malfoy Manor before the Battle of Hogwarts. A battle you are going to lose. I have come to save you.
HARRY/VOLDEMORT turns. She meets his eyes.
It was Rodolphus Lestrange, Bellatrix’s loyal husband, who on return from Azkaban told me who I was and revealed the prophecy he thought I was destined to fulfill. I am your daughter, sir.
From Harry Potter and the Cursed Child, we know that Voldemort had a child with Bellatrix Lestrange:
DELPHI: I am your daughter.
HARRY/VOLDEMORT: If you were my daughter, I'd know of you.
DELPHI looks at him imploringly
DELPHI: I am from the future. The child of Bellatrix Lestrange and you. I was born in Malfoy Manor before the battle of Hogwarts. A battle you are going to lose. I have come to save you.
Delphi speaks Parseltongue, looks like Bellatrix, and has prodigious magical talents, and so is probably correct in believing she is his daughter.
As such, he must have had sex at least once.