The company, which is aimed at 16-24 year-olds in particular, said its main womenswear range of dresses and jackets, as well as its new menswear website, also saw strong sales.
Pre-tax profits jumped 129% to Â£14.3m in the six months to August.
It also benefited from successful marketing campaigns, especially on social media.
"We have... stepped up our activity on social media on Facebook Live and on Snapchat and a content drive on Instagram has helped us pass the two-million follower mark in the UK," the company said in its statement.
This has been a large part of the company's success, analysts said.
While it is still much smaller than rival Asos, Boohoo has been particularly savvy about "communicating with its core 16-24 year-old customers," said retail analyst Kate Ormrod from research firm Verdict.
It uses bloggers and "influencers" to showcase its designs.
"As the customers mature, keeping them interested will be a challenge," Ms Ormrod added.
Asos has 12 million active customers, while Boohoo, which started in 2006, now has 4.5 million active shoppers.
The fashion industry as a whole as been trying to attract the lucrative plus-size customers, said Ms Ormrod, and that's something that Boohoo has done well.
"They haven't always been offered the most fashionable styles and it's a strongly growing market."
The joint chief executives, Mahmud Kamani and Carole Kane, said there was "robust growth across all regions and continued momentum in new customer growth".
Revenue rose 38% in the UK, 41% in Europe and 93% in the US.
It plans to introduce a new range of children's clothing, as well as a small maternity range.

Maurice Weir told a court he witnessed a "bloodbath" when hounds from a local hunt club attacked the birds on his land in Loughgall, County Armagh.
He sued the Countryside Alliance over the intrusion by the Kinnego Grange and Canary Hunt Club's dogs in 2009.
The judge rejected defence arguments that Mr Weir had fabricated the claim.
Giving evidence to the High Court in Belfast, Mr Weir described how he emerged from having lunch on 7 February, 2009 to discover "a bloodbath" on his Kinnego Road  property, with dead and injured birds lying on the ground and in dogs' mouths.
He said up to 15 hounds had broken into his pigeon lofts and aviaries and attacked highly sought after homing pigeons, some who could make their way back to Northern Ireland from France,
He had been planning to use the birds to set up a small stud business and sought damages for the killing of his pigeons, consequential loss, the cost of repairing his aviaries and a further payout for distress and injury to feelings.
His barrister claimed the hunters were negligent in failing to control their dogs.
Lawyers for the Countryside Alliance claimed that no hounds from the hunt came into contact with the birds on the day in question, but the judge ruled that that Mr Weir was an honest witness whose account was corroborated by others at the scene.
She ruled that the hounds had been on his property, gained entry to the lofts and aviaries and, on the balance of probabilities, killed the pigeons.
She awarded him £59,580 in damages and £2,500 for distress and injury to feelings.
"To these figures will be added the appropriate interest on general and special damages together with costs," the judge ruled.
The Countryside Alliance has six weeks to decide if it wants to appeal the verdict.
Strong sales of plus-size and petite clothes have helped boost profit at online fashion retailer Boohoo.
[NEXT_CONCEPT]
A pigeon fancier who lost 59 racing pigeons after hunting dogs strayed onto his property and killed the birds is to receive more than £60,000 in damages.