Investigators from Baja California's state police are in a small town in the central part of the state following up on a possible sighting of missing Fallbrook businessman Joseph McStay, his wife and two young children, it was reported.The McStays were last heard from Feb. 4. Their white Isuzu Trooper was found near the San Ysidro border crossing around the same time -- the same day surveillance video in the area captured two adults and two small children walking hand-in-hand toward the turnstile leading into Tijuana.Afredo Arenas, an international liaison collaborating with U.S. authorities, told The San Diego Union-Tribune that seven investigators arrived in the town of El Rosario Tuesday night. Employees of a restaurant reported seeing the family there shortly after the McStays were reported missing.A relative told the newspaper that a waiter mentioned a prominent birthmark on the youngest child's forehead, adding credibility to the potential sighting.Sheriff's deputies conducted a welfare check on the McStay's Fallbrook home Feb. 15 at the request of a concerned relative. They found no signs of foul play, but the family's two dogs were left in the back yard and other evidence seemed to suggest the family didn't plan to be gone long.Relatives have said they don't know why the family would have willingly fled the country.Joseph McStay, 40, ran an indoor water foundation business, his wife Summer, 43, stayed in their recently purchased home with their 3- and 4-year- old sons.Sheriff's investigators searched the family's computer and found records indicating they made inquires about traveling to Mexico with children shortly before they disappeared. Investigators also searched through the family's finances and found no signs of distress.