IHS Holding Ltd. shares fell on their debut in New York after an initial public offering valued the pan-African telecom-tower operator at almost $7 billion.

The shares slumped 18% to $17.12 as of 12:45 p.m. local time on Thursday. The owner of more than 30,000 phone masts across Africa, the Middle East and South America had earlier sold stock at $21 each, compared with a range of $21 to $24, according to a statement before the market opened.

The deal raised $378 million for the company to fund growth plans.

“Proceeds will be used to build within our current markets, and move into new markets,” Chief Executive Officer Sam Darwish said by phone. “We have high growth markets that require new sites.”

IHS is based in Mauritius, making the initial public offering the largest in the U.S. by an African business. The company has been expanding to take advantage of improved connectivity in emerging markets, while wireless operators have been selling off their masts to specialist firms to raise cash.

The group’s Africa markets are Nigeria, Ivory Coast, Zambia, Rwanda and Cameroon.

“We look at markets in Asia and Latin America and if a new opportunity to acquire a portfolio of towers present itself, or go with a large greenfields project, we will definitely do that,” Darwish said.

MTN Group Ltd., Africa’s largest mobile-phone company, was the biggest shareholder in IHS with a 29% stake before the IPO. The Johannesburg-based firm sold some shares. French investment firm Wendel SE, which owns 26%, is holding on to its entire shareholding.

MTN will have just over 85 million shares after the listing, the company said. They are valued at $1.46 billion based at current prices.

“The listing gives MTN a strong liquidity platform that will support the group’s strategy of accelerating growth in its African markets, de-leveraging and strengthening the balance sheet,” CEO Ralph Mupita said.

By Loni Prinsloo and John Bowker