HighTower, a fast-growing aggregator of financial advisor firms, announced Tuesday it added a team of former Merrill Lynch advisors to its expanding roster of partner firms.

The new addition, Simmons Wilkes Group in Portland, Me., had more than $500 million in assets under management and a clientele with average household assets of between $3 million to $6 million. The firm's focus is on investment management and family wealth planning.

The principals coming to HighTower--Edward Simmons, Gibson Wilkes, Blake Wilkes and Michael Simmons--join as managing directors and partners. Combined, they had more than 30 years' experience with Merrill Lynch.

HighTower, a Chicago-based independent, advisor-owned company serving high-net-worth investors and institutional clients, has acquired $19 billion in assets since it launched in late 2008. It now comprises 20 advisor teams and 44 partner advisors, and spans 11 offices across 10 states.

Mike Papedis, HighTower's managing director of business development who oversees recruiting, says the folks at Simmons Wilkes Group contacted HighTower directly before they were handed off to one of the firm's recruiters. "They were attracted to our partnership model and have been following us for awhile," he says. The principals at Simmons Wilkes couldn't be reached for comment.

Partner firms who join HighTower are issued a chunk of equity in the company, and can earn more equity after joining as part of its partnership model.

Papedis says 25% of HighTower is owned by the principal members of its advisory teams.

HighTower has made a steady stream of high-profile deals the past two years, and expects that trend to continue in 2011. "We plan to do more deals than we did last year," Papedis says.