Get a bottle asap and wards if your team didn't buy them. Dominate the rune control and gank the side lanes. Once you're 6 you should be able to gank him with ease. Keep in mind he's a squishy int hero and you're capable of locking him down for quite some time
the problem is that is so hard to get to him,i an only do it with ult
Like others have said you have a couple of ways to deal with him. If you have a mana battery you can counter some of his harass, and if you have a bottle you can just heal. You'll be getting more mana than you can use between these two so just drop mines and use your passive to harass him. Back up when he has the mana to combo you. Maintain rune control, gank side lanes with haste/invis, keep your HP up, and when you're 6 enjoy the easy gank whenever he comes out of his tower. Even then you can tower dive him if he drops below 2/3 health.