Chipotle Mexican Grill announced Wednesday it's begun to search for a new CEO, with current Chief Executive and Founder Steve Ells becoming executive chairman.

The restaurant chain's board has formed a committee to help find a new leader, Chipotle said. On the committee are directors Robin Hickenlooper and Ali Namvar, as well as Ells. Recruitment firm Spencer Stuart will also assist in the search efforts.

Chipotle shares rallied on the news, climbing about 6 percent in premarket trading. Late in the day Tuesday, the stock jumped and closed up 4 percent.

Bill Ackman's Pershing Square, which is the company's largest shareholder with an 11 percent stake, pressed for Hickenlooper and Namvar to join Chipotle's board at the end of 2016.

"I am incredibly proud of Chipotle and our people — and grateful to our loyal customers — and while we are continuing to make progress, it is clear that we need to move faster to make improvements," Ells said in a statement.

Once the search for a new CEO is complete, Ells said he will focus primarily on innovation.

"As we work hard to restore our brand, I believe we can capitalize on opportunities, including in areas such as the digital experience, menu innovation, delivery, catering, and domestic and international expansion, to deliver significant growth," he explained.

Ells founded the restaurant chain in 1993, and has since played multiple roles, serving as co-CEO at one point. In 2009, he shared the role with Monty Moran. Last year, he became the sole CEO of Chipotle once again.

Chipotle has struggled of late to win customers back after reports of a norovirus outbreak at its Sterling, Virgina, restaurant circulated in July, once again dinging the chain's reputation. The company has faced numerous foodborne illness outbreaks since 2015.

"While a new CEO is not a silver bullet, the move gives Chipotle a chance to look again at its strategy and its approach," GlobalData Retail Managing Director Neil Saunders told CNBC via email.

"This is desperately needed, for along with the various health scares consumers are increasingly bored with an offer that has never really evolved," Saunders said.

In its latest quarter, Chipotle's same-store sales missed analysts' expectations, sending shares tumbling once again. Back in 2015, Chipotle shares soared above $700 apiece, when the company was viewed as a pioneer of the fast-casual concept in the restaurant industry. On Tuesday, the stock closed under $286.

Some of the chain's latest turnaround initiatives include a refreshed advertising campaign and a nationwide rollout of queso dip, which was criticized by some customers. Chipotle has since hinted at other new items, such as salads and desserts, to come.

As of Tuesday's market close, Chipotle shares have fallen more than 24 percent this year.