Thomas joined Freeserve two years ago to create an access product management team and to manage the company's narrowband and broadband products.
She replaces Peter Cowley, who left the company in December.
Freeserve portals managing director Jon Gisby said: "Both our content and ISP member base are growing fast and we really need someone like Caroline to make sure we direct that growth and development in the right way."
Before joining Freeserve, Thomas worked for eight years in new media in a number of jobs including at BT's interactive TV and internet division, and before that for Compaq in the US.
Thomas said: "We are looking at a whole raft of exciting new product developments and offers coming up, and I'm looking forward to the challenge of developing the portal further to improve our overall customer experience."
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