Following fellow early Facebook employees CTO Adam D'Angelo and VP Matt Cohler, Facebook's head of data and analytics Jeff Hammerbacher will leave the company. Cohler left for a prestigious partnership at VC firm Benchmark Capital. D'Angelo left — or was encouraged to leave — in order to find a project more suited to his interests. VentureBeat, which broke the Hammerbacher news, doesn't know why he's going. One thing all the departures have in common: They've come after COO Sheryl Sandberg's arrival. "Scaling up is hard and it's not as much fun not to know everyone you work with," she told employees when she joined the company. We're wondering if it won't be harder for Facebook founder and CEO Mark Zuckerberg than he might think — what will he do without all his friends?

We know Zuck was close to Adam D'Angelo. They went to High School together and even built the digital music software that first igniting Zuckerberg's entrepreneurial imagination back in his teens. Cohler was employee number five at Facebook — there when the company was one room big. Zuck recruited Hammerbacher, whom he knew from Harvard, to join the company from a presumably well-paying gig at Bear Stearns. With all his friends leaving, oon Zuckerberg won't have any Woz- or Allen-like buddy at the company.