The robbery was reported Thursday at about 3:30 p.m. when an 18-year-old East Palo Alto resident agreed to meet the suspect, identified as 21-year-old Denmark Copeland of Redwood City, in the 2400 block of El Camino Real.
Police said the victim had listed four cellphones for sale on Facebook and went to a parking lot to meet Copeland. The victim got into Copeland's car and Copeland allegedly pulled a gun and demanded he hand over the phones.
The victim complied and got out of the car without injury.
Police identified Copeland as a suspect and started surveillance on all residences associated with him.
At about 9 a.m. officers saw him walking in the 300 block of McEvoy Street and arrested him. He was allegedly carrying a replica handgun in his waistband and evidence connecting him to the robbery, police said.
Copeland was booked into San Mateo County Jail on suspicion of robbery.
Anyone with information about the robbery has been asked to call Redwood City police Detective Joe O'Gorman at (650) 780-7147.