Faizullah, there is some nice trekking in the area of Mae Hong Song and east of there at Soppong. Try checking in at Cave Lodge, many walks from there, and plenty of caves to visit. Another area where i spent two weeks (twice) was Umphang where i managed to wander of in different directions each day. To get to Umphang take a sawngtheaw from Mae Sod and five hrs later you will reach the end of the road at Beautiful Umphang. PhuKradung is a park not so far from Loie. You can camp at the top and do a few hikes from there and you may be lucky and see some wild animals.
Here is a site that recommends treks, and i have been to most of these places and have had no problem exploring on my own