The group reported revenues for the six months to June of US$51mln compared to US$36.8mln for the same period in 2015.
Xl also saw underlying profits grow to $17mln, a year-on-year increase of 32%.
“We continue to execute our business plan and diversify,” said chief executive Ory Weihs.
“The company’s position as a leading performance marketing company is allowing us to implement our know-how, expertise and technology, as well as to further expand into additional verticals and markets.”
The AIM-listed firm’s largest customer accounted for just 7% of revenues for the period, down from 11% last year.
It also managed to reduce its reliance on business from Scandivania, with only 48% of its revenues coming from the region, compared to more than half in 2015.
The group added that in the first half of this year it has rolled out some enhanced features for its systems, including Palcon, the firm’s proprietary content management system.
XL has told investors it will publish the full audited interim results in September.
Shares were up 3.3p, or 4.4%, to 78.3p.