Pop singer Andy Grammer (left) got close with fans at the Hatch Shell during Mix 104.1’s MixFest on Saturday, which also featured performances by Train and former Berklee College of Music student Gavin DeGraw. Grammer said on Twitter that he sent a “ton’’ of messages to local fans through the site after the show. Lucky them. The acts must have been staying at the Revere Hotel because DeGraw was spotted there during the weekend, as was Matchbox Twenty frontman Rob Thomas, who played at a pre-show party on Friday night. Thomas was seen in the Revere’s Emerald Lounge.